Bee Line I

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Let’s get into the cockpit of a honey bee worker (to borrow an evocative metaphor used by Jochen Zeil) and try to figure out how she is going to solve a problem in navigating and communicating: finding a food source, getting back home, and informing her nest mates how to find the same food.  This is a problem that thousands of bees solve every day in every honey bee colony.  Their ability to solve it explains a lot about their ecological success and their importance to our agricultural systems.

As we shall see, the bee does the navigation part by using visual features of the environment: the sun and earth-bound landmarks. She does the communication part by encoding navigational information into body movements that have been called a “dance language.”

To appreciate the difficulty of the problem, consider that it is common for bees to fly to food sources a mile or more from the nest.  Let’s use two kilometers to keep things in round numbers, and because the metric system really does make it easier to do calculations in your head.  Given that a bee is about a centimeter long, food that far in the distance is two hundred thousand body lengths away. Or you can think about it in travel time.  Bees fly about eight meters per second, so it takes two hundred fifty seconds to fly two kilometers.  That’s a little more than four minutes.

Why does it matter how far the bee has to travel? The key issue is that for a typical flight distance of two kilometers, neither the food source nor any landmarks around it are visible, smellable, or detectable by the bee in any other way. You of course face the same problem that the bee does if you want to set a course for a grocery store two kilometers or more from your home. Unless you live in a flat treeless plain where the IGA sign is visible down the road, all you can see at the beginning of your journey are features of the environment in the immediate vicinity of your starting point, but most of those—at least the ones fixed to the ground and not up in the sky—will soon disappear from view as soon as you are underway.

The solution to this problem, for both bees and people, is to rely upon either the sequence of landmarks (trees, bushes, hills) visible along the way, or on a directional reference, such as the sun, that can be continuously checked during the trip.  Neither of these sources of navigational information is inherently easy to use.  Landmarks corresponding to particular routes have to be learned, and for a long route it would be necessary to learn a long sequence of landmarks. Not only that, but the landmarks will look different on the way out to the goal than on the way back, and so the bee (and you) will need to learn how to recognize and use them going both ways. As for the sun, its position relative to the route is not constant thanks to the rotation of the earth, so you need to know how to compensate for this rotation.

Once the bee is back home with her load of food, the plot thickens. The next part of her challenge is something that she can do but that no other organism other than human beings can do—she has to tell her nest mates which way to go to get to the same food source.  She does so with a series of body movements—a “dance” it has been called—while a small group of her nest mates pay close attention.  This happens in total darkness, but it can easily be seen by us if the colony is in a glass-walled observation hive. The dance takes place on the vertical sheets of comb. The overall structure of the dance varies in specific ways according to the direction and the distance the bee has flown to reach the food. Many have noticed that the dance looks like a repeated reenactment, on foot and at a miniature scale, of the flight the dancer has just taken.

The bees following the dance, after attending it for a few cycles of repetition, will peel away, leave the nest, and search for the same flower patch that the dancer had come from.  Many will get there, and may come home and do dances of their own, leading to a rapid buildup of foragers in the patch.  The resemblance of this communication system to the way humans communicate—encoding information about experience in behavioral actions (vocalizations or gestures in our case)—led the discoverer of this system, Karl von Frisch, to call it a “dance language”.

For further explanation of how bees solve these problems, and how we know how they do it, stay tuned….

What is it like to be a loggerhead turtle?

A new paper in the Proceedings of the Royal Society B by Mansfield et al. reports the first long-term tracks of newly hatched loggerhead sea turtles after they enter the ocean.

Here is the abstract:

Abstract

Few at-sea behavioural data exist for oceanic-stage neonate sea turtles, a life-stage commonly referred to as the sea turtle ‘lost years’. Historically, the long-term tracking of small, fast-growing organisms in the open ocean was logistically or technologically impossible. Here, we provide the first long-term satellite tracks of neonate sea turtles. Loggerheads (Caretta caretta) were remotely tracked in the Atlantic Ocean using small solar-powered satellite transmitters. We show that oceanic-stage turtles (i) rarely travel in Continental Shelf waters, (ii) frequently depart the currents associated with the North Atlantic Subtropical Gyre, (iii) travel quickly when in Gyre currents, and (iv) select sea surface habitats that are likely to provide a thermal benefit or refuge to young sea turtles, supporting growth, foraging and survival. Our satellite tracks help define Atlantic loggerhead nursery grounds and early loggerhead habitat use, allowing us to re-examine sea turtle ‘lost years’ paradigms.

This is a fascinating example of how informative simple observation can be.  Consider the mystery of the sea turtle life cycle.  The babies hatch from nests on the sandy beaches of the eastern seaboard of the U.S. and various Caribbean islands.  Upon hatching they make their way to the sea, swim far offshore, and are lost from view.  Bigger turtles can be observed at sea, caught in fishing nets.  Some can be caught and sampled, and their DNA compared with turtle populations from around the world.  This suggest that turtles from the eastern U.S. somehow make their way to the other side of the Atlantic , even as far as the Azores, as they mature. Then years after hatching, adults return to the same beach where they were born.  Mothers haul themselves ashore, dig a nest in the sand, and lay dozens of leathery eggs.

What exactly happens in the years between first entry into the ocean and the return to the beach where hatching occurred.  Do they drift passively?  Swim in particular direction? Some combination?  If only we could just ride along and watch?

That, in effect, is what this recent paper has tried to accomplish, at least for the first several months in a hatchling’s life. The study used solar-powered satellite transmitters which are small enough to ride along on the carapace of the turtle, and powerful enough to send a signal that reports where the turtle is, if not let us actually see the world from the turtle’s perspective.  Still, knowing where the turtle is tells us a lot.

The study reports tracks from 17 turtles that hatched on a beach in northeastern Florida and then were tracked for up to 220 days, for distances ranging from 200 to 4300 kilometers.  See the tracks superimposed on maps of the North Atlantic color coded to show variation in ocean depth (top) and sea surface temperature (bottom):

Image

Notice that the tracks (the white filaments in the upper map, the dark filaments in the lower) initially follow the course of the gulf stream, which may suggest that the turtles simply drift with prevailing currents.

Over the longer term the tracks show that turtles depart from the Gulf Stream, and not in random directions.  Instead they move east and south rather than north or west, which takes them into the “North Atlantic Subtropical Gyre,” the great swirling pool of water in the western North Atlantic. That they move in this direction when departing the Gulf Stream is an essential step in their life cycle, because it moves them toward the vast Sargassum seaweed beds in the Gyre that will be their feeding and sheltering grounds as they grow.  Let’s have a closer look of one of the turtles as it veers away from the Gulf Stream:

Image

The paths relative to ocean currents suggest that the turtles are not only passively drifting (though they may do a lot of that), but also making directed movements.

Other evidence about the turtle and their Umwelt comes from the tags: the batteries stayed fully charged.  Since the power for the charging came from solar cells, this suggests that the turtles spent a lot of time near the surface rather than diving down to swim or feed.  This may have been to aid swimming (because of the drag from the tags on their back) or, more likely, to bask in the sun’s warmth.

How do they do this?  How do the turtles guide themselves on a course that would have defeated many human mariners during our history of oceanic exploration? What is it like to be a loggerhead turtle during its life cycle?

More specifically, what features of the environment can tell a turtle, bobbing in the vastness of the ocean, far out of sight of land and carried an unknown distance by the mighty Gulf Stream, which direction to turn to head toward the Sargasso Sea (which more or less coincides with the Gyre), let alone how to steer back home?

We don’t yet know the answer to this, but the leading hypothesis is that the turtles can take a reading from local features of the earth’s magnetic field that vary in a systematic way over the whole of the ocean.  Reading the magnetic coordinates specifies a heading that is appropriate for their goal.  Lohmann and colleagues (2001) published experimental evidence for this idea, by giving neonate sea turtles (in a laboratory) the magnetic coordinates for different parts of the North Atlantic around the Gyre, and observing that they adopted magnetic headings that would be appropriate for each of those regions.

That study by Lohmann et al. suggested two amazing things about the Umwelt of the loggerhead turtle.  First, that like von Uexküll’s tick, they do not need to have a very sophisticated understanding of their task to solve a complicated problem.  In the turtle’s case, it is as if they come into the world programmed with a list of magnetic headings corresponding to different magnetic map coordinates.  Nothing that requires them to have experienced it before, and certainly nothing in the way of a comprehensive understanding of ocean currents. The other amazing thing is that the turtles’ knowledge  base is specific to the part of the globe where they live and their species has evolved.  They do not have a generic or abstract knowledge of any part of the ocean or the earth’s magnetic field except the North Atlantic. They are creatures of their particular place, and their brain and behavior are tuned to that part of the world.

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Lohmann KJ, Cain SD, Dodge SA, Lohmann CMF 2001 Regional magnetic fields as navigational markers for sea turtles. Science 294, 364–366. (doi:10.1126/science.1064557)

Mansfield KL, Wynekan J, Porter WP, Luo J. 2014 First satellite tracks of neonate sea turtles redefine the “lost years” oceanic niche. Proc. Roy. Soc. Lond. B. 281 (1781) 20133039. (doi:10.1098/rspb.2013.3039)

Ceci n’est pas une abeille

As someone who loves bees, I deeply appreciate all of the attention given in the popular press to the plight of honey bees, their importance to agricultural and natural ecosystems, and the efforts of scientists to explain their decline. I am distressed, however, by how common it is for these pieces to be accompanied by photographs of insects other than honey bees.

First some examples, then an explanation of why it matters:

From Huffington Post 26 February 2014

Screen shot 2014-02-26 at 11.40.02 AM

(This is not a bee but rather it is a fly)

From Treehugger.com 26 July 2013

Screen shot 2014-02-26 at 8.25.00 AM

(This is a bee but it is not a honey bee; probably it is a bumble bee.)

From Global Research 9 August 2011

Screen shot 2014-02-26 at 8.34.31 AM

(This is a bee but it is not a honey bee.)

From Miami New Times 27 December 2013

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(This is not a honey bee; I don’t know what it is–some kind of a wasp perhaps? Here is the Flickr page with the original. Not much help except that the photo was taken in Australia.)

From CNN.com 2 April 2013

Screen shot 2014-02-26 at 8.54.54 AM

(This is a video about honey bees, but the still image on the start screen is a bumble bee)

From Yahoo News Canada 9 July 2013

Screen shot 2014-02-26 at 9.30.11 AM

(This is a bee, but not a honey bee; perhaps it is some kind of sweat bee?)

From Blouin News 23 January 2014

Screen shot 2014-02-26 at 10.24.33 AM

(An article about honey bees, but this image is probably of a carpenter bee)

From International Business Times 29 March 2012

Screen shot 2014-02-26 at 10.30.19 AM

(Another fly–a bee-mimicking hover fly)

ETC ETC ETC ETC…….

So why does it matter? One reason is that these photos betray an superficial understanding of nature: an understanding based on surface similarities and not on the details that are the evidence of the wondrous and beautiful variety of nature.  Take the last picture, for example.  It is not a bee at all, but a hover fly, one that natural selection has shaped to resemble a bee closely.  The resemblance probably functions to deter predators who would love to eat a fly but hate to eat a bee. You can actually see, if you look closely, the ways in which the insect in the picture is not a bee:  the “pollen balls” are blobs of color on the abdomen and not clumps of pollen on the hind legs; there is one wing on each side of the body rather than two (ok, the paired wings are hard to see in the bee pictures); the antennae are short stubs instead of long and bent at the midpoint as in bees (particularly evident in the bumble bee in the second picture from the top). To give them different names you have to know about their differences. There is beauty in both the similarities and the differences between the fly and the bee that it mimics, but this is lost by just calling every bee-like thing a bee.

The other reason is that knowing the names of things deepens our appreciation of them. Naming and appreciating not only honey bees but also bumble bees, hover flies, carpenter bees and all the rest might increase our motivation to protect all of these insects with their varied ecological roles.  This is something I have long felt, but others have expressed this better, especially Terry Tempest Williams.  For example:

London: In An Unspoken Hunger you say, “Perhaps the most radical act we can commit is to stay home.” What do you mean by that?

Williams: I really believe that to stay home, to learn the names of things, to realize who we live among… The notion that we can extend our sense of community, our idea of community, to include all life forms — plants, animals, rocks, rivers and human beings — then I believe a politics of place emerges where we are deeply accountable to our communities, to our neighborhoods, to our home. Otherwise, who is there to chart the changes? If we are not home, if we are not rooted deeply in place, making that commitment to dig in and stay put … if we don’t know the names of things, if don’t know pronghorn antelope, if we don’t know blacktail jackrabbit, if we don’t know sage, pinyon, juniper, then I think we are living a life without specificity, and then our lives become abstractions. Then we enter a place of true desolation.

I remember a phone call from a friend of mine who lives along the MacKenzie River. She said, “This is the first year in twenty that the chinook salmon have not returned.” This woman knows the names of things. This woman is committed to a place. And she sounded the alarm.

This is from an interview here: http://www.scottlondon.com/interviews/williams.html.

(h/t to KE for the reference to Terry Tempest Williams.)

Parsimony and the Umwelt concept

This project is about opening up the cognitive world of another organism to study and understanding. Before we get too far along, an important ground rule is in order. While I will unabashedly invoke hypothetical constructs that can also be applied to human cognition, labeled by terms such as “representation,” “computation,” “decision-making,” “emotion,” and the like, I am also going to be extremely careful about how I use and define such terms. This is important even for the study of human cognition, to which these terms may first have been applied, but it is even more important for the study of animal cognition. One reason for caution is that a surface similarity between two things (say, something an animal can do and something people can do) is not evidence that they are caused by the same underlying process. Another reason is that in nature, in general, the way things actually work is often simpler than might appear, and it is reasonable to assume that cognitive abilities of animals are simpler than those of human beings, even when the behavior they mediate is superficially similar.

This notion that things may be simpler than they appear is a foundational principle in science. The principle goes very various names: the Parsimony Principle, Ockham’s Razor, etc. Scientists use it all the time explicitly or implicitly. (So, by the way, do car mechanics, forensic investigators, and historians, if not conspiracy theorists or ufologists.) The basic idea is to prefer the simplest possible explanation for a given phenomenon, unless the evidence forces you to accept a more complex explanation.  This general principle is embraced not as a simple article of faith, but because it is a good guide to understand–things are often simpler than they appear.  However, they are not always simpler in they way we think they are, and sometimes they are not simple at all, so the parsimony principle by itself is not enough.

An aside on Ockham’s Razor, named after the theologian William of Ockham (c. 1287 – 1347). I looked Ockham up in the Stanford Encyclopedia of Philosophy, and learned two interesting things. One is that the most common formulation of Ockham’s razor does not actually appear in his writings, although the underlying sentiment does. That common formulation goes, “entities must not be multiplied beyond necessity” (entia non sunt multiplicanda praeter necessitatem). According to Wikipedia, that formulation was written not by Ockham but by one John Cork in 1639. However, Ockham did write something very similar: “Plurality is never to be posited without necessity” (Numquam ponenda est pluralitas sine necessitate). The more interesting thing I learned in the Stanford Encyclopedia of Philosophy article had to do with Ockham’s criteria for determining when we would have positive evidence for affirming the existence of things. He gave three criteria, saying, “For nothing ought to be posited without a reason given, unless it is self-evident (literally, known through itself) or known by experience or proved by the authority of Sacred Scripture.” What intrigued me about this is that in some cases what we know because it is self evidence or by experience may contradict the authority of Sacred Scripture, so retaining all three of these criteria seems a violation of Ockham’s Razor. Perhaps Ockham couldn’t have known how thoroughly experience (i.e. science) would come to undermine the truth claims of Sacred Scripture about how the world works.

Back to ethology and cognition. A version of the parsimony principle was articulated by an early student of animal behavior, Conwy Lloyd Morgan, in reaction to the anthropomorphic theories advanced by some of his predecessors. Often known as Lloyd Morgan’s Canon (or simply Morgan’s Canon), this goes as follows: “In no case is an animal activity to be interpreted in terms of higher psychological processes if it can be fairly interpreted in terms of processes which stand lower in the scale of psychological evolution and development.” Morgan’s Canon greatly influenced the development of the sciences of animal behavior during the 20th century, especially in psychology. Indeed, it was only with great reluctance that psychologists in the middle to late 20th century allowed themselves to speculate about cognitive processes that might intervene between the stimuli impinging on the animal’s sense organs and the responses that the animal produced. In the extreme, the “radical behaviorists” such as Watson and Skinner claimed that hypotheses about cognition were untestable and hence unscientific. As we shall see, this proved incorrect. To be fair, it was not entirely unreasonable to doubt that one could make inferences about unobservable mental processes on the basis of the stimuli and responses that could be observed and measured. However, the evidence, won through the ingenuity of experimental psychologists (of humans as well as animals), has allowed the rigorous testing of hypotheses about mental phenomena.

Another foundational principle shaped the thinking of the zoologically trained European scientists who invented the field of ethology. In fact this principle is central to this whole project of trying to enter the world of the honey bee. The principle is the Umwelt concept, which was developed and applied to animal behavior by Jakob von Uexküll. This is the notion that each animal inhabits its own, species-specific subjective world, perceiving just those features that matter to its existence, and producing just those actions that matter for its survival. (As an aside, the word “Umwelt” is one that means “environment” in German, but it is not the only one. “Umgebung” is also used. In fact, Umgebung was the word, found in Goethe, that was rendered in English by Thomas Carlyle as “environment.” See discussion here about how this happened. I find it intriguing that English, a language with Germanic roots, couldn’t just borrow the German word intact rather than inventing a word with French roots, but I suppose that reflects the politics of nationalism and cultural envy.)

In any case, the original formulation of the Umwelt concept by von Uexküll contained a principle of parsimony regarding the complexity of the processes underlying the responses of animals to the environment.  But it was more a descriptive than a normative principle: von Uexküll was making a claim about the way the world is rather than about the logical necessity of this reality. In particular, he argued that one could  explain apparently complex behavior in terms of a simple set of reactive mechanisms.  The Umwelt concept, as it is described in many animal behavior text books, is equated to the idea that animals live in their own species-specific perceptual worlds, which may not be identical to our perceptual world.  This is indeed an important part of the story, but it is only half of the story: the Umwelt of an organism encompasses not only the perceptual world, or Merkwelt, but also the “effector world,” or Wirkwelt, the set of actions that it is capable of performing. Beyond this, an animal’s Umwelt is organized into what von Uexküll called “functional cycles,” which von Uexküll considered fundamental units of behavior. Each functional cycle consists of a simple perceivable feature of the environment and the action that it “releases” (to use the term adopted by later ethologists). It is the identification of a simple set of functional cycles underlying apparently complex behavior that shows the Umwelt concept to be a parsimony principle.

The example that von Uexküll used to illustrate this concept is the ability of the common tick to “hunt” for mammalian prey.  This might be regarded at first glance as a complex behavior, whereby the female tick positions herself strategically in a location where prey might pass, then leaps onto them at the right moment and then navigates to a part of the body suitable for biting and sucking on blood. Von Uexküll suggested that it can be explained by positing just four functional cycles: first, the animal senses gravity and climbs upward in vegetation and then stops; second, it waits for the smell of butyric acid, a common component of mammalian body odor, which causes it to drop; third, tactile contact with fur releases crawling; fourth, warmth (from contact with skin) releases biting and sucking. If the tick misses at step two or is brushed off at step three, then it just starts at step one.  This is a highly impoverished Umwelt:  the predator’s entire “knowledge” about mammals is represented by three stimuli: the smell of one chemical, the touch of fur, and warmth.  But, as von Uexküll said, “the very poverty of the world guarantees the unfailing certainty of her actions, and security is more important than wealth” (von Uexküll 1934).

One of von Uexküll’s critical insights is that we need to view the animal as the subject as well as the objects of the processes that cause it to behave the way it does.  Adopting this stance requires us human observers to unshackle our imaginations from the constraints of the very rich Umwelt that we inhabit.  It requires an act of imagination to picture what it might be like to be a tick (or a bee). Often the Umwelt of a given animal will turn out to be simpler than might appear, as in the case of the tick and many other species studied by the early ethologists such as Niko Tinbergen.

But simpler does not merely mean that an animal’s Umwelt is a reduced or stunted version of the human Umwelt. In fact, ethologists have discovered that animals may be capable of responding to sensory stimuli which to us are completely undetectable by our sense organs or are meaningless even if we can sense a crude tingling in the presence of the stimulus. Examples are the ability to detect polarized light in blue sky (most insects and arthropods), electrical fields (several groups of fish and also bees), magnetic fields (several bird species), ultraviolet light (most insects and many birds), infrared light (pit vipers), ultra-high frequency sounds (bats and some birds), ultra-low frequency sounds (elephants). Furthermore, quite apart from merely sensing such stimuli, what animals do with the information they contain boggles the mind–at least it boggles my mind.  Three examples: the ability of pigeons to navigate home after being displaced to an unfamiliar location a thousand kilometers away; the ability of a bat to emit ultrasonic chirps and then analyze the returning echos to chase down and capture flying insects; the ability of a honey bee to measure the distance and direction of a flower patch (even if she has flown an indirect path to get there), then fly home and report this in movements of her body we call the dance language.

Adopting the Umwelt concept has been liberating in another way; it has enabled the elucidation of how different animal species may interact when their sensory worlds overlap.  An example is the realization, in the 1990s, that many birds analyze each other’s plumage by integrating across ultraviolet as well as visual wavelengths. This led to the realization that what is bright to our eye may not be bright to a bird’s.  In an earlier, and even more dramatic example, the discovery that bats hunt their prey using echolocation in the ultrasonic frequency range was followed by the discovery that many insects (including some moths, lacewings, and mantids) can hear these calls and undertake evasive escape maneuvers.  As I wrote in an earlier review of this topic, “Thus, the Umwelten of predator and prey interlock in a grim ballet set to a score that only the dancers can hear” (Dyer and Brockmann 1996).

Bats, with their dazzling ability to live in a world of sound, have played a disproportionate role in illustrating the Umwelt concept. And it is no coincidence that they served as the straw man (there, I said it) in Nagel’s argument for the futility of knowing the nature of other minds. But that’s a topic for another day.

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References cited:

Dyer, F.C., J.A. Brockmann.  1996.  Orientation, sensory processes, and communication.  In:  Foundations of Animal Behavior  (Ed. by L.D. Houck and L.C. Drickamer).  Chicago:  University of Chicago Press.

Uexkull, Jakob von 1934. Streifzuge durch die Umwelten von Tieren und Menschen. Berlin: Springer-Verlag. (Translated as: A stroll through the worlds of animals and men, in C.H. Schiller, ed., Instinctive Behavior, pp. 5-80. New York: International Universities Press [1957]).

 

 

How to be a honey bee: Apis dorsata (3)

At tropical latitudes the period of twilight is very abbreviated.  That’s because the lower your latitude (the nearer the equator), the more nearly perpendicular the descent of the sun relative to the horizon.  At high latitudes, in the summer at least, the sun descends at a shallow angle, so it still lights the atmosphere for a long time after the disk disappears below the horizon.  (Above the Arctic Circle or the Antarctic Circle, the sun may just graze the horizon and thus stay in the sky all night.)  In the tropics the sky goes from very bright to very dark in a matter of minutes. This meant that I did not have long to wait to see the effect of the sun’s disappearance on the foraging activity of “my” Apis dorsata colony.

I had arrived an hour or so before sunset, which I would come to learn was the most active time of day for this colony.  Dozens of foragers were leaving or arriving at the nest each minute. The arriving bees, most of them bearing pollen on their hind legs, quickly commenced to perform dances on the  curtain.  Each dancer was attended by a half dozen or so bees paying close attention to the dancer. Overall I could see many hundreds of bees engaged in a seething choreography of pas de six (ou cinq ou sept).

As sunset approached, drone bees–the males of the colony, whose only role is to seek  opportunities to mate with queens produced by other colonies–started to appear in the curtain and embark on their mating flights.  Drones first massed in the top layer of the curtain about 20 minutes before sunset, and then issued forth by the hundreds in a nearly synchronized launch. Somewhat heavier bodied than workers, their buzzing was louder and lower in pitch than that of the workers. Their departure amplified the insectan soundtrack accompanying the sun’s disappearance.

As the sky darkened over the next 30 minutes, outgoing trips by foragers ceased, and all that I could hear (and see when I briefly turned on my light) were the bees returning from the field–workers with their last load of nectar or pollen and drones that had been unsuccessful in finding a virgin queen.  The moon was still low in the sky, and the end of the solar twilight led to a deep darkness of night.  For a moment, the bee colony in front of me had ceased all flight activity, and all I could hear was the quiet rustling of wings of bees moving in or under the curtain.

I hoped to see whether the bees would resume their foraging when the moon came up, but I had to figure out how actually to observe any activity that occurred.  I couldn’t see bees in the darkness, and didn’t want to use an artificial light for fear that it would affect their behavior.  I had brought a headlamp, and a red acetate filter to tint the beam of light–European honey bees don’t see as well in red light as human beings do, so that provides a way of observing bees while they experience darkness.  But I didn’t even want to risk shining red light on the colony.  In a moment of improvisation, I decided that I would simply listen for the departing bees.

I sat on the ground with my back to the nest, my head a foot and a half away from the curtain.  Straight ahead at eye level was a tangle of vegetation, and past that the moon’s disc was visible, fragment into pieces by the leaves. If I looked up at a forty-five degree angle I could see a patch of open sky that was already taking on the silverish glow from the rising moon.

For the next ten minutes I sat in a nearly silent world, hearing only the rustling of the colony, the chirping of some insects in the betta lands.  I was far enough from Sirsi or any highways that I heard no sounds of humanity.  The moon climbed higher and brightened the sky and the surrounding countryside. Finally I heard the first departure.  A sudden onset of humming that rapidly faded as a bee left the colony behind me, passed my head, and sailed off into the sky.  Then another a few seconds later.  And another.  I checked my digital watch, shielding its greenish glow with my hand.  I blindly scrawled the time in my notebook.  At the same time I clicked three times on a handheld tally counter I had brought with me. Another departure, another click.  Another, then another.  Over the next fifteen minutes, I kept count the best I could, and wrote down totals at one-minute intervals to record the beginning of these nocturnal flights.  I was confident that I could distinguish the sound of each individual departure.

To my amazement, the departures got more and more frequent until I was recording as many as 20 bees leaving per minute, a rate that rivaled what I had seen during the day.  Clearly this nocturnal flight activity was something more than just a haphazard tendency of a few bees to leave the nest because the moon brightened things up a bit.  What I could not yet know is whether any bees had returned to the nest–perhaps they were just confused and were attracted to the moon as if it were a big streetlamp.  Amidst the noise of the flight activity around the nest, there was buzzing that I thought could be coming from returning bees, but these sounds were harder to make out than were the launches of the departing bees. The only way to know was to turn on my light and look.

Three or four times during my scientific career, I have experienced moments of discovery that evoke feelings of complete astonishment:  in the moment of observation, I see a phenomenon that is utterly surprising, and at the same time I know that I am the first person ever to see it.  This was one of those times.

Rather than using my headlamp, I used a small penlight that was also fitted with a red filter.  I turned it on, and was amazed to see a nocturnal version of the curtain in a state very similar to what I had seen when the sun was up.  It was covered by bees engaged in dance communication.  Arriving bees bore large pollen balls on their legs, and performed dances for retinues of followers.  The presence of pollen on the dancers’ legs was an important observation by itself because it was proof that the bees had gone to a flower, collected the resource, and flown home with it.  Pollen foragers shed their pollen after they dance, so there was no way to explain the presence of pollen except by the hypothesis that they had just returned from a flower patch.

A quick scan of the nest revealed a few things.  First, at least ten dances were going on.  Second, every single dancer was carrying pollen.  Third, by looking at the direction and distance signaled in the dances, I could infer that the pollen had come from two distinct flower patches.  As in the European honey bee, a Apis dorsata dancer performs a series of repeated “waggling runs” in which she runs in a straight direction while waggling her body from side to side.  The direction of the food is signaled in the orientation of the repeated runs relative to gravity.  The distance to the food is signaled in the duration of each repeated waggling run: the farther the food, the longer the waggling run.  It was easy to see by eye that the dances clustered into two groups in which the waggling directions were over 90 degrees apart.  Fourth, given the distances signaled–which based on my estimate corresponded to a flight of at least several hundred meters–the bees doing the dances must have been previously familiar with the patch they were signaling.  There simply hadn’t been enough time since moonrise for them to search for an unknown location then marshal enough nestmates by their dancing to produce the large corps of dancers that I saw when I first turned on the light.

So, in a matter of minutes, with a few simple observations, I had found that Apis dorsata foragers fly by moonlight (as British naturalists had reported a century earlier), that they find flower patches that were previously familiar to them (presumably by seeing landmarks learned during the day or on previous nights), that they can land on flowers and harvest pollen, that they can then find their way back to the nest, and, most remarkable, that they do nocturnal dances that signal the location of these flower patches.

My mind was flooded with questions, and I realized that I was in a position to get some evidence bearing on some of these questions even on this first night of observation.  I knew I had to get organized quickly and make the measurements that would lead me to answers.

However, I did allow myself to savor that moment.  To appreciate the beauty of the night–the tropical air cooling with the departure of the sun, and the land drenched with moonlight.  To stand in awe of the creature before me: heedless of my awe, my curiosity, and my pride at my moment of discovery, the bees simply were doing what they had been doing for millions of years–scrambling to get the precious bounty of floral resources faster or in greater quantities than other flower visitors in their neighborhood.  It mattered to them not at all that they were breaking the rules by using their diurnal eyes to fly by moonlight, or that they were challenging human notions about the limits on the sophistication of insect behavior.

How to be a honey bee: Apis dorsata (2)

The roads out of Sirsi lead directly into the countryside, with no fringe of suburbs to pass through.  For that matter, Sirsi isn’t much of an “urb,” although it is very densely settled. It is a market town in the Uttar Kannada district of the state of Karnataka.  The population when I lived there was, I believe, well over a hundred thousand. The tallest building was a five-story hotel near my house. Otherwise it was a two-story town.

A warren of streets, lined by shops selling products useful to an agrarian population, lead into a central market square dominated by a large bus station, a post office, and more shops and restaurants. During the days the streets are invariably clogged with traffic both wheeled (buses, lorries, cars, three-wheelers, scooters, motorcycles, bicycles) and unwheeled (people and cows and more people and more cows). The sheer density and the propensity of Indian drivers to honk incessantly makes the town very noisy during the day.  My house was on the immediate outskirts, where there were a few neighboring houses, the hotel, a petrol station, and a government school, but I still felt surrounded by humanity (and by cows).  Not so much as when I lived in the huge urban centers like Bangalore and Bombay, of course, but I still felt relieved when I left for the countryside, like a diver coming up air.

I steer my motorcycle on the road leading west out of town into the green of the land around Sirsi.  Sirsi sits on the western slopes of the Western Ghats, the long chain of small mountains running along the western side of the Indian subcontinent.  It is about 50 km west of the lushly forested crest of the Ghats , but it still gets a lot of rain, about a hundred inches a year.  Most of this occurs during the monsoon season from May through August, as winds saturated with moisture move onto the land and have their water squeegied out by the mountain chain.  The rain, although it falls only during half the year, supports a rich plant community.  The undisturbed forests are classified as “semi-evergreen”–they are green year-round, but many trees shed their leaves and take on a drier appearance.

Most of the land around Sirsi is cultivated rather than naturally forested, but you still feel like you’re in a forested land.  That’s because agriculture here is dominated by a cash crop, arecanuts (betel), which come from an elegant palm grown in dense groves in low-lying terraces. Also in the valley bottoms are rice paddies, emerald green in the rainy season.  The surrounding hills are planted with coconut groves, or are used as “betta lands”–these are private lands  kept in a park-like state with lots of trees, and used for grazing cattle or harvesting tree products for food, fuel, and building materials.

I’m heading back to the farm where, earlier in the day, I had been shown the rock bee colony at ground level.  My destination is only about 5 km from town.  I turn from the paved road and follow the dirt track into Mr. Hegde’s betta land.  I stop at a live fence, a tangle of woody shrubs that had been planted to keep unwanted grazing cows out, gather the equipment that I had placed in my carryboxes, and walk toward the bees.

It is about 4:30 pm.  My previous visit was in the late morning, near the heat of the day.  Apis dorsata colonies are typically fairly inactive during midday.  That’s because the plants that provide them with food tend to produce their nectar and pollen only during early morning and late afternoon, when the air is cool and has higher relative humidity. Compared with what I had seen earlier, I came upon a very different scene when I worked my way through the vegetation surrounding the colony.  The curtain, still thick with bees, seemed overlaid by a froth of activity–other bees walking on top of the curtain, and many flying bees coming and going from the nest where the vegetation provided openings to the sky.

Even from a distance, the active portion of the curtain looks darker than the parts where there are no bees walking or coming or going.  The curtain bees normally hang with their wings filling up the space between their interlinked bodies, but when other bees walk across their backs they lower their pale orange abdomens and close their tinted wings.  The overall effect is to reflect less light to the distant observer. Up close, you have to watch for a while to see the order in all the activity taking place on the surface of the curtain.  The arriving bees, or at least most of them, are carried brightly colored pollen balls on their hind legs–oranges, yellows.  They land with a silent impact, pause briefly, then organize themselves to begin dancing.

Many of the bees walking on the curtain are involved in dance communication.  Within minutes of sitting down, I spot a dozen dancers, each surrounded by an audience of 5-10 followers.  Apis dorsata dancers, compared to those of other species, waggle with a lazy rhythm, shaking their bodies side to side slowly enough for the human eye to see with barely a blur. As in all honey bees, a given dancer performs multiple waggling runs during her dance, aiming each one in the same direction as the last, and waggling for a consistent duration each time.  Between runs the dancer turns herself around and begins again. Some of the dancers perform short waggling runs–a second or so–while others waggle for as much as 10 seconds each time. Sometimes dancers pause after a series of runs, then resume. Sometimes you can see a dancer stop altogether and dive into the curtain, presumably to shed her pollen in preparation for the next flight to the food. Where dances continue, you can see followers occasionally break away from their own choreography, and then peel off to undertake flights of their own, presumably searching for the sources indicated by the dancers.

As I watch, and as the sun gets lower in the sky, I notice that the moon, nearly full, is apparent above the horizon in the eastern sky.  That’s what I’m here for.  I’m looking forward to seeing what happens after the sun sets altogether.

How to be a honey bee: Apis dorsata (1)

K.M. Hegde and I reached the end of the dirt track riding on his Bajaj scooter. We were here to meet a man, also with the surname Hegde, who was to show us a nest of Apis dorsata. K.M. Hegde, my friend and guide in India, had put the word out that I was looking for nests of this remarkable bee. I was interested in any nest, but especially one close to ground. Most colonies construct their nests in inaccessible locations such as rock overhangs, tall trees, or the upper stories of buildings. I was hoping to study the bees at close range, without the worry of ladders, platforms, or climbing gear. Now it appears that we had found a nest that would enable me to do this.

We greeted the other Mr. Hegde and chatted for a bit in a mix of English (K.M. Hegde and me) and the local dialect of Kannada (K.M. Hegde and the other man). Then we walked through the open betta land toward a stream bed. Just before the stream was a tangle of vegetation that consisted mostly of the foliage of a fallen fig tree. Fig trees, being the contortionists of the plant world, don’t necessarily die when they fall, so long as some of the roots remain connected to the ground. The main stem of this tree was now horizontal, suspended about a meter off the ground by upper limbs and by root buttresses that supplied nutrients to the still living tree. As we approached, I could see through the leaves that a large Apis dorsata nest was hanging from the underside of the stem.

An Apis dorsata nest can be thought of as a chimera of wax and insect and honey and pollen. Beeswax is secreted in tiny flakes from glands on the underside of the abdomens of some of the worker bees. These flakes are harvested by the millions and molded by other workers into the two-sided sheet of hexagonal cells that make up the comb.  Apis dorsata colonies build their comb in the open, placing wax bits on the underside of an overhanging structure, then growing it downward, adding to the size as the number of bees in the colony increases.  The comb is where the queen lays eggs, which develop into larvae and then, after they reach full size, form pupae and undergo metamorphosis in the way caterpillars turns into butterflies. The comb is also where the colony stores pollen and nectar collected from flowers.  The whole affair is protected by a curtain of living bees that hang quietly, legs interlocked, in an orderly array. Behind the curtain is the queen, doing little but eating and laying eggs,  and and a work force of bees caring for the queen and her brood. The living portion of the assemblage may include 40,000 or more bees, weighing almost five kilograms, or as much as a house cat.

I had already spent time in close proximity to Apis dorsata colonies, and even more time working with the European honey bees (Apis mellifera) while beekeeping, and I knew that the main way to stay safe with bees is to act as little like a predator as possible–no fast movements, no vibration of the nest or its support structure, no injury to the workers that could lead to the release of alarm pheromone. I was confident that I could approach with little risk that I or my Hegde companions would be stung by defenders. Still, an Apis dorsata colony is an intimidating presence, so I was particularly careful.

As I picked my way through the foliage, I could see the full semi-circular shape of the nest, extending a meter along the supporting fig tree trunk, and hanging almost to the ground.  There was little flight activity–an occasional arrival or departure, but otherwise the protective curtain of workers remained quiescent, rippling just slightly from the adjustments by the workers, or from the effects of the breeze where the curtain hung loosely away from the comb.  The curtain appeared to be several bees thick and completely concealed any view of the wax comb, but on hot days like this one the bees in the curtain relax their grip on each other to loosen the weave of the curtain, enabling dissipation of metabolic heat.

I approached cautiously, paying close attention to how the colony reacted. One of the intimidating things about an Apis dorsata colony is that all of the bees in the curtain can see anything that approaches from their side of the nest. My looming shape caused thousands of curtain bees to twist in place to fixate both compound eyes on me.  A compound eye of compound eyes. The faster I moved the larger the quantity of bees that turned toward me. I knew that if I moved too fast some would leave the curtain and fly toward me and possibly sting me. As it was, my approach caused the curtain as a whole to produce a collective display that is common when threats intrude.  A wave of buzzing  originated at one location on the curtain and then traveled outward across the curtain like ripples on a pond, then repeated four or five times.  I think of it as being akin to the rattle of a rattlesnake, warning a predator of the risk. I paused on hearing this, and waited to the colony calmed down.

In slow motion I sat myself on the ground next to the colony.  I could hear the colony: rustling of wings against wings, the transient hum of the arriving and departing foragers, the steadier, quieter hum of bees standing on the curtain beating their wings to produce cooling air currents.  I could smell the colony: the rich, earthy-sweet aroma of wax, honey, pollen, and insects. In the leaf litter a few centimeters below the colony, dark red weaver ants from a nearby colony, each a centimeter in length, patrolling for opportunities to capture worker bees.  Even though A. dorsata workers must be at least ten times more massive than weaver ant workers, a group of ants can easily subdue a bee, and thus the weavers are major predators of bees.  The bee colony had other visitors as well–a jumping spider watching from a nearby twig, a gecko poised on the fig bark near the attachment of the nest, a small cloud of tiny stingless bees cruising along the curtain looking for ways to sneak in to steal honey.

As I sat there watching, absorbed in the presence of this superorganism, I was aware that K.M. Hegde and the other Mr. Hegde who owned the land were expressing amazement at my boldness.  This species of honey bee (“Hejjenu,” or “big bee,” in the local dialect) is valued as a major source of honey in South Asia, but it is much respected for its potential to unleash fearsome stinging attacks.  The only people who come close to a colony are the honey hunters who intend to drive the workers away with smoke and fire and to cut down the comb to squeeze the honey from it.  So it is simply not a common sight for someone to sit close and just watch the bees.  I tried to explain that it was a  matter of understanding the animal’s thresholds and what kinds of stimuli to avoid presenting.  But I think they viewed me as some kind of bee whisperer.

The timing of this Apis dorsata colony’s appearance in my life could not have been more perfect.  The day was in April, a few days before the full moon.  And it was to observe the bees by moonlight that was one of my primary goals in coming to India.  To free the Mr. Hegdes to go about their work for the day, I got up to leave.  After getting permission from the landowner to return in the evening, K.M. Hegde and I left to travel back to the town of Sirsi, where I lived.

Observed: What is it like to be stung by bees? (Part II)

The first sting came on my bare hand. I felt the one-two punch of a typical pain reaction: an immediate flash, not really experienced consciously as pain, and a powerful temptation (quelled in the moment) to jerk my hand back. This was followed a beat later by a duller stab that surged into consciousness, an elevation of my pulse, a hot shiver that raced up my spine and then throughout the rest of my body. Both stages were intensified by the surprise that should have been no surprise, and then by a second sting that landed very near on my hand to the first. Unfortunately I had to finish tying a knot and could not drop what I was doing lest the attack escalate into a much worse disaster.

I freed one hand long enough to scrape away the sting and associated tissue that each bee had left behind. Then as I went back to the knot-tying I started feeling more stings. Two or three more on my bare hands, then one on my back. My face and head were protected by a beekeeper’s hat and veil, but otherwise I was wearing a long-sleeved cotton shirt and long trousers rather than heavy beekeeper’s coveralls. The stings of the large bees easily penetrated the weave of the shirt and thus the skin of my back where the cloth was against my skin. Another sting landed on my back, then another. I smelled the tell-tale ripe-banana scent of the alarm pheromone. I could see bees on the nest becoming more agitated and taking flight. I could hear bees already in the air increase the pitch of their buzzing, indicating that their metabolic rates had increased, their wings were beating faster, and they were flying faster. I could see them flying faster around me and at me.

Another bee stung my back, then another, while others landed on my hands. Dozens of were standing on my cloth-covered arms, and presumably all over my back. In the midst of it all I noticed that some of these bees were buzzing their wings and tapping the tips of their abdomens against me without everting the sting itself. Even in the moment I couldn’t help but think like a scientist: I wondered if they were doing this to intensify the aversive impact of the experience for me while letting other bees actually do the life-sacrificing stinging: something like the way a rattlesnake’s body divides the labor between the pain administered by the bite and the auditory warning administered by the rattle.

As I hastily finished my task, occasionally taking time to dislodge stings left in my hands, I stopped counting the impacts, which kept coming. Each next sting didn’t add proportionally to the accumulated pain. The pain was already plenty intense enough to engender an anxious feeling bordering on panic, not so much from the pain as from the anxiety about what this attack could become. A mass stinging attack, especially from this species, can be pretty scary. Knowing that flailing my arms and running away would make me a more attractive target, I walked slowly away, flicking stings from my hands, and pulling the cloth of my shirt away from the skin of my arms and torso. I hoped that this would pull the stings out of my skin and minimize the amount of venom injected.

Hundreds of bees were in the air around me, pinging against my body, my hat, and the screen of my veil. At regular and frequent intervals new stings would land in every part of my body, although fewer in my legs because I was wearing baggy trousers. I tried to remove them as fast as they arrived, but couldn’t keep up. My goal was to get to a pickup truck parked about 50 meters away, and then get in so that I could remove the stings. Throughout every stage of this, my friend Tom was no more than 4 meters away. We had been working together, and he was clothed with the same level of protection from stings as I was. He walked along with me, making sure I was okay. I thought I detected a bit of a smile as if my predicament, and the slow-motion tugging I was doing to pull my clothing away from my body, was comical to him. At no point did he get stung. The first stings had landed on me, and that’s where the alarm pheromone had begun to accumulate, so that’s where the bees focused their attention.

We reached the truck and got in, after brushing or waving away as many bees as possible. Whether or not they had found me as their target, the bees that entered the truck with us quickly got confused and flew toward the windows as confused insects do. We cracked open the windows and let them out, and then I set about removing my veil and as many stings as I could.

I sank back in my seat and felt the warm, pulse-racing glow of my body’s reaction to the venom. Fortunately I am not allergic to bee venom, or that first sting could have been disastrous by itself. However, to receive so many stings–a conservative guess is that I received as many as 50 in about 5 minutes–produces a complex cascade of biochemical reactions as the cellular damage at the site of each sting releases enzymes and other molecules that travel throughout your blood stream and cause inflammation and changes in blood flow elsewhere in your body. Once the initial pain subsides, the sensation is rather pleasant, a warm sub-feverish rush.

This attack did not happen with Apis mellifera, the European honey bee used for beekeeping in North America and most of the rest of the world. It happened with the giant Asian honey bee. This bee goes by the common name of “rock bee” because of its tendency to nest on rocky overhangs, and by the Latin name Apis dorsata. In Thailand, where the events I described took place, it goes by the name “Peung Leuang, which means “Royal Bee,” the name that I think fits it best. This is the bee in the photograph on the main header of this web site (an image taken in Sri Lanka, where the bee is called by the local name “Bambara”).

These are magnificent bees. They do not nest in enclosed cavities as do the western hive bee, but in the open. The colony builds a single sheet of two-sided wax comb measuring a meter or more across, attaching it to an overhanging rock, a heavy tree limb, the underside of a balcony, or any of many other human-made structures. The comb, where eggs are laid to be reared into the next generation of bees and where honey and pollen are stored, is protected by a living curtain of workers. Colonies tend to aggregate their nests in certain (presumably safe) locations. Here is a picture that I took of a banyan tree near Bangalore, India, that, at the time, had at least 186 Apis dorsata nests hanging from its limbs. Click to make it bigger.

DorsataBeeTreeBangaFull

This is an extremely dangerous animal. Their nesting biology is one reason why, but not the only reason. The workers are as large as hornets. The large bodies mean that their stings are longer and their venom sacs hold more venom than other honey bees. The exposure of the nest, and the large mass of nutritious larvae and honey, means that this bee is a tempting target for many predators, and this has probably led to natural selection for a high degree of vigilance and a readiness to sting when disturbed. The protective curtain gives thousands of workers a direct view of approaching threats, and if you wave your hand in the vicinity of the colony, thousands of bees remain in the curtain but turn to stare at you. It is very easy to provoke them to launch an attack.

Why, it is natural to ask, would I be in a position to bring on such an attack? Well that’s a story for another time, but the short answer is that Tom and I were in the midst of capturing the nest, bees and all, for removal to another site for study. I had done this before, and had a lot of prior experience with this species. I knew what to do without panic if an attack did happen, and a reasonably high level of confidence that I could work closely with them without causing an attack.

To wit:
CatchingDorsataChiangMai

dorsatasirsibarechest

Observed: What is it like to be stung by bees? (Part I)

Skipping right over the cheap jokes (“It frickin hurts!”), let’s explore contexts where it is less or more likely that you’re going to get stung. Let’s further specify the main character in this drama: bees in the genus Apis. We’re not going to talk about yellow jackets (genus Vespula), which are wasps and not bees, even though it is those persistent yellow and black nasties–familiar guests at late-summer picnics–that form most people’s conception of what a bee is. (Yellow jackets: smooth body surfaces, strongly contrasting yellow and black markings, diet of other insects plus scavenged human food, common at picnic tables. Honey bees: bodies covered by fuzz, golden brown and black markings, diet of pollen and nectar from flowers, rarely if ever found at picnic tables). As entertaining as it may be to read about getting stung by either species, let’s keep focused and ponder the joys of being stung by honey bees.

When would this not be likely to happen? It is unlikely to happen at a picnic table, even in the rare event that a bee were there. It is also unlikely to happen if you were to disturb a bee as it visits a flower. Try this at home–as a bee lands and probes a flower for nectar, reach out and stroke it with a finger. Feel the fuzz on its thorax. It will not sting you. If it does anything, it will fly up and then simply land again, or maybe fly off to another patch.

Try this too, but be really careful or leave it to an expert: using your thumb and forefinger, grasp a honey bee’s two pairs of wings, which fold over its abdomen when it lands. If you do it just right and get both pairs of wings between your fingers, the bee won’t be able to bend her abdomen around and sting your finger. (Don’t do this with a bumble bee, because bumble bees have a more flexible abdomen.) You can hold the bee this way as long as you want without being stung so that you can look closely at it. You can study the beautiful compound eyes (which are all the more beautiful through a microscope), wrapping the sides of the bee’s head and part of her face, so dark in color that they are almost black, and covered by a dense forest of stiff bristles (stiffer than the fuzz on the body) pointing directly outward from the convex surface of the eye. You can study the the antennae, each with a pronounced geniculate kink partway along its length, flexing and reaching for stimulation. You will see the three pairs of legs, which will be reaching for something to stand on, and observe the differences among them: the front and middle pairs shorter and more or less like generic insect legs; the hind legs longer, and with a special modification just past the inverted knee–a flared structure with long curved bristles that can accumulate big clumps of pollen that the bee combs off her body as she visits flowers. (This structure is the “corbicula”–bees that carry pollen on their hind legs, which is not true of all bees, are the group called the “corbiculate” bees).

Study the tip of the abdomen, and you may see the bee’s sting (or “stinger” as it is commonly known) flicking in and out of its chamber. The sting is normally concealed (along with the back end of the alimentary canal and the opening of the reproductive tract) by the plates of the exoskeleton that form the tip of the abdomen. A bee that is alarmed can open these plates and evert the sting. A bee held in the way just describes tends to be alarmed, and so you will probably see the sting flicking out. To the naked eye it looks like a fine hair narrower and shorter than an eyelash. You might see a small droplet of venom formed at the tip of the sting.

Having studied the bee, now just let her go. You might think that her first move upon release would be to fly back and sting you, but if you have picked her up off a flower, she is very unlikely to do anything other than to land again and start feeding.

In the vicinity of the hive, the bees’ reactions to these kinds of disturbances, or ones that are much less drastic, are wholly different. If you try the following exercises at home, then I suggest you wear a beekeeper’s hat and veil, and possibly the rest of the bee suit including gloves. We’ll consider a commercial bee hive as the context of this exercise, although the bees’ behavior would be similar should you approach a hive in a natural nest cavity such as the hollow of a tree. The typical bee hive is a large, usually white box about a foot and a half across the front, two feet front to back, and three to five feet tall. A full-sized hive might have 30,000 to 50,000 bees in it. The foragers are coming and going from the entrance, a slit at the bottom of the first story. Other bees linger at the entrance rather than flying. Some of these may be facing inwards. If so, then it is likely that they will be standing still beating their wings in a blur. A collective exhaust fan. Other bees may be facing outwards. They seem vigilant. They react to movement, including incoming foragers, orienting with a quick lunge but then resuming their stations when the stimulus passes. These are guards. If anyone is going to sting you, it will be these bees.

Wave your hand quickly in front of the hive and then bring it to a stop. Guards standing at the entrance will react with an orienting movement. A few may fly at your hand, perhaps traveling all the way to it. Wave again. Same thing. Now wave and keep waving. This draws more bees, and they not only fly to your (gloved) hand but sting it. Assuming you’re doing this with a gloved hand, you can take a closer look at the marvels of the honey bee sting apparatus, which was tugged out of the bee’s body when she flew away. The delicately pointed sting is stuck in the glove, caught there by microscopic barbs like those on a harpoon. Attached to the sting itself is a sac containing venom, and a small package of muscles and neural tissue.

Honey bee sting apparatus

The muscles do two things–they work the sting deeper into your skin, and they pump in the venom. The sting is actually not simply a pointy thing, but rather an exquisitely organized piece of biological engineering. It is split along its length into two halves, which can slide back and forth relative to each other. One side slides into your skin, then its barbs catch and anchor the sting as the other side is pushed in deeper. The force for the pushing comes from muscles at the base of the sting, and the rhythm is generated by a simple neural circuit that sits quietly inside the bee’s body until the apparatus is torn away from the bee’s body, and from an inhibitory neural connection that has kept the sting’s neural circuitry quiet until now. Other muscles squeeze the walls of the venom sac to pump venom down a tube that passes through the two halves of the sting.

Hold the sting to your nose. You will detect a somewhat cloying scent–the alarm pheromone–that has been compared to bananas in a certain stage of ripeness. The comparison is apt because one of the molecules in the alarm pheromone is butyl acetate, which is also emitted by ripe bananas. Generally speaking, a pheromone is a molecule emitted by one animal that influences the behavior or physiology of another one. The alarm pheromone gets its name because it makes other bees more likely to sting. You are in a position to prove this true by waving your gloved hand gently in front of the bee hive–the bees at the entrance will become very agitated, and several will fly up and at you, and are likely to sting the glove again in the location of the previous sting.

Now you have experienced being stung, and had the opportunity to look closely at the bee doing the stinging, fully protected from any actual discomfort. Let’s change the situation….

To be continued….

Observed: pollinators (plural)

Over the weekend I visited a garden center with a friend and sat for a while in the sun admiring a plant that turned out to be a kind of hydrangea. Unlike the kind of hydrangea with the huge globular white or lavender-colored inflorescences, the flowers on this one were arranged on large cone shaped clusters. The individual flowers making up this inflorescence also varied in size (from a few millimeters to a centimeter and a half across), color (pink vs white), and size (wide open petals vs tiny cups). Not being a botanist or a horticulturalist, I was fooled by the cone-shaped inflorescence into thinking it was a butterfly bush. But Google set me straight, so I called the garden center, described the plant and told them where it was on the property, and learned that it is a variety called a Pinky WinkyTM hydrangea. How embarrassing for the hydrangea.

Here’s one:
Pinky Winky hydrangea

But this isn’t a story about hydrangeas. It is about pollinators. Pollinators plural. As in lots of them, and not just large numbers but also a large variety. We sat next to that plant for nearly an hour, and during that time we must have seen 15-20 different species of insects on that bush and on other nearby hydrangeas.

There were honey bees, to be sure, but the honey bees were not exceptionally more numerous than were the several other kinds of insects. There were also other species of bees that varied in size and (I happened to know, because I do know a little more about insects than I do about horticulture) social behavior. There were bumble bees (genus Bombus), which are bigger than honey bees but live in colonies of 50-200 as compared to the colonies of 15,000 to 30,000 that honey bees form. There were carpenter bees (presumably Xylocopa virginica), North America’s biggest bee, which live a solitary existence in which females have complete responsibility for burrowing tunnels in wood and provisioning their young with food collected from flowers. There were some tiny sweat bees (probably genus Lasioglossum), which form small cooperative colonies that nest in the soil. There was a big, fast-flying insect that I think was a bald-faced hornet (a wasp, Dolichovespula maculata)–an insect predator that also visits flowers for nectar.

Then there were flies–ones that looked like house flies, ones that looked like flesh flies, ones that looked like (and probably were) hover flies. Obviously I don’t know my flies very well. Then we saw two tiny, delicate flies that wore metallic green suits. They might have been “long-legged flies” (family Dolichopodidae). They were standing on a leaf and not exploring the flowers, perhaps because long-legged flies weren’t interested in what the flowers had to offer; these flies get their protein by eating other insects (smaller ones) rather than from flowers.

Except for the long-legged flies, this horde was busily engaged in exploring the big dangly inflorescences that adorned the bush. Most repeatedly buried their faces in the florets to get nector. The honey bees and bumble bees brushed pollen into the clumps forming on their hindmost pair of legs. The pollen was a silky taupe color. Some insects seemed to favor bigger florets, some smaller ones.

The variety of pollinators present on this one bush was striking, and so were the numbers, but the numbers weren’t overwhelming. One or two insects per inflorescence on a bush that may have had 30 big inflorescences. Plus the nasty little long-legged flies waiting to pounce on something smaller than them. Or maybe they were a male and a female engaged in some other bit of biology. Nor did the pollinators interact aggressively. Like honey bees that seem to ignore others of their own kind within the same patch, these pollinators just went about their business and barely seemed to notice each other if they happened to have an encounter on the same inflorescence.

The pollinators were peaceful with each other, and also were oblivious of the two large mammals who were watching and occasionally reaching out to stroke the bees as they fed, to show it could be done. (It has to be said that these two mammals were paying a lot more attention to each other than to the bees and flies engaged in their own serious business.) Although all of the bees present on the plant had stings and should have known how to wield them, none seemed ready to use their stings while collecting food on the flower.

It would be a very different matter, by the way, if you tried to disturb a bee close to its nest.