Honeybees - starting at the end

When starting a lecture on animal communication, most people would probably leave the honeybees for last. Only because their communication has some unique linguistic features most other animal communication lacks. Namely: symbols. Honeybees have an elaborate language for communicating the location of food and shelter through dance. We have decoded most of it due to the Nobel Prize-winning work of an Austrian named Karl von Frisch.
(Herr Dr. von Frisch looks great in lederhosen, don't you think?).
Karl von Frisch discovered that European honeybees (Apis mellifera) could communicate the precise location of a resource by dancing.
(Can you imagine anything more wonderful? What if we communicated through dance alone? Tell me that doesn't sound like fun.)
The dance has two components: an angle and a distance - all the bees need to find a location. The angle is communicated by the angle at which the bee takes a waggle run relative to straight up. Outside, this angle corresponds to the angle of the resource relative to the sun. The length of time the dancing bee spends waggling corresponds to the distance to the food resource. When a forager bee comes back from collecting food, she will dance, and in the dark hive, other bees will surround her and follow her dancing movements repeatedly, extracting the location information from her movements. Then the foragers will set out to the location she indicated. This is the basic formula for the dance language. Other aspects, such as sharing nectar samples, floral odors, and vibrational signals also play a role in telling the other bees the type and quality of the food resource.

The dance language is also used when a swarm (a newly budded bee community ready to start their own hive) needs to find a hollow cavity to nest in. Scouts that find a suitable cavity dance to communicate its location to the other workers. The better the cavity, the longer a bee will dance for it. This length of time spent dancing is key to the collective decision-making of the swarm, which must take off all at once and move together if they are to survive. The longer a bee dances for a location, the more recruits she will get to check out the possible new home, and the more bees will come back to dance for that location. Eventually, almost all the scouts will be dancing for the preferred location. Once they have reached a quorum, the bees take off to colonize the new home.

So that's the fantastic story of the honeybee dance language. My question is: why so sophisticated? Why do honeybees alone among invertebrates demonstrate use of symbols? Why are honeybees considered the pinnacle of insect communication? Honeybees themselves are not very remarkable insects. Physiologically, they are similar to their bumblebee and wasp brethren in brain capacity. One thing that they do have that many other bees and wasps lack, however, is eusociality.

Eusociality is the term we use to describe social animals where there is:

1. Reproductive division of labor - some individuals reproduce while others give up or delay their own reproduction
2. Overlapping generations - individuals from previous generations live together with individuals from the current generation
3. Cooperative care of young - non-reproductive individuals rear other individuals' offspring

Only a handful of animal species fit this definition. In many ways, honeybees wrote this definition. A single queen bee lays all the eggs in the hive, while the workers (sisters and offspring of the same queen) do all the work of gathering food, feeding the young, constructing, maintaining, and guarding the nest. The honeybee hive functions as a super-organism, with each individual doing its part to serve the hive. The critical phase in the reproduction of this super-organism is the swarming stage, when the hive buds, and a group of bees and a queen must choose a new nest. For the European honeybee, which requires a suitable cavity, this selection process is very important to deciding the future fate of the swarm. You could imagine that the selective pressure would be extremely high for an efficient way of communicating the location of a possible new nest site.

This is only one theory that might explain the evolution of such complex behavior in honeybees rather than other species which do not exhibit swarm-founding. Indeed, the selective pressure for more advanced communication must increase with increasing levels of cooperative behavior. Is this true? Do we find other examples in the animal kingdom of advanced communication in conjunction with cooperative behavior?

Animal Linguistics Series

My linguist friend has invited me (ok maybe I volunteered) to give a guest lecture to her class. In this lecture, I will cover a number of examples of animal communication and compare and contrast these communication systems with those of humans.

Linguistics has always seemed very interesting to me. I might even classify myself as a word geek. I collect new words like shiny insects, pinning them down by using them often. I am very good at crosswords.

Communication in the animal and particular the insect world, however, is rarely possessed of such nuance as actual words. Nevertheless, animals say a whole lot with chemical, sound, and visual signals. Some animal communication systems are surprisingly complex.

To prepare for this lecture, I'm going to go through a few outstanding examples of animal communication over the next several days. Enjoy!

Leviticus

Spur-throated Grasshopper, originally uploaded by OakleyOriginals.

Leviticus 11 is a chapter of Hebrew law dealing with what is and is not permissible to eat as meat. God prohibits eating of pigs, shellfish, birds of prey, lizards, etc. These animals do not fit the cleanness requirements of God's law, and so Israel is not to consume them. Insects are on the list too (vs. 20):

"All flying insects that walk on all fours are to be detestable to you."

Putting aside for a moment the anatomical inaccuracy of saying that insects "walk on all fours" (who really says "walks on all sixes" anyway?), the message is clear: don't eat bugs. But then there's an exception (vs. 21-23):

"There are, however, some winged creatures that walk on all fours that you may eat: those that have jointed legs for hopping on the ground. Of these you may eat any kind of locust, katydid, cricket or grasshopper. But all other winged creatures that have four legs you are to detest."

The Orthoptera are on the menu! The order Orthoptera includes grasshoppers, locusts, crickets, and katydids. Leviticus gives us the easiest sight ID characteristic for this order: jumping legs. If you want to be fancy you can call them "saltatorial" legs. Check out this handsome fellow in the photo above. Nice saltatorial legs, eh?

So, why are Orthopterans invited to dinner, but nobody else from Insecta? This is a difficult question. Some say that they are hygienic, less likely to carry parasites than other insects. They are good, meaty insects too, nutritious. Some say that they aren't as close to the ground because they hop, and so they are cleaner. Others say that they are clean because they are exclusively herbivorous. Others remember that locusts are a major agricultural pest problem in the near east, and in some years the locust swarms would blot out the sun and consume every fruit, leaf, and stick in their path, leaving only the locusts themselves to be consumed by the devastated farmers.

Personally, I like thinking of the Orthoptera as the skilled musicians of the insect world. A vast majority of the Orthoptera chirp, sing, drum, or rattle to call their mates. Few other insects make such pleasing music. Perhaps the singers are invited to dinner to remind the Israelites about their role as praisers of God, commanded to make a joyful noise to him who gives life to all the creatures that swarm on the ground.

Roach reflexes

I've told you about the spectacle that is the Great Insect Fair Cockroach Races. Roaches are impressive runners. Apparently the fastest roach ever recorded sprinted at an amazing 3.4 miles per hour, which, when you're only 2 inches long, is lickety-split.

Perhaps you have had the surreal experience of being sure that you have stamped on an offending cockroach, only to find that he has Houdini'd his way out from under your shoe and is now across the room and disappearing under your fridge. How is it- you ask yourself- that roach-kind has invented teleportation?

Roaches, it turns out, have mastered the art of escape not with magic, but with fast reflexes.

Cockroaches are characterized by the presence of two appendages called cerci (SIR-see, singular cercus) on their last abdominal segment (read: butt). In many species, the cerci are covered with delicate sensory hairs for chemoreception or mechanoreception and act kind of like antennae for the rear end of the insect. The cerci of cockroaches are exceptionally sensitive. They are sensitive enough to pick up the tiny air currents created by your foot sweeping toward them threateningly. The sensitive cerci send a signal up the ventral nerve chord directly to the nerve center of the thorax controlling the roach's legs. Only three neurons stand between the cerci and the legs. Accordingly, the roach can react in less than 70 milliseconds. A blink of an eye is 300-400 milliseconds.

It is grace, is it not, that God gives cockroaches this kind of speed? They are universally hated and feared, constantly persecuted by stomping feet or chemical warfare. But at least the cockroach has been given the reflexes to escape from impending doom with near-clairvoyant speed.

Antennation

Insect antennae are sophisticated organs that can perform many functions for insects:

• Olfaction (smell)
• Gustation (taste)
• Mechanoreception (feeling)
• Hygroreception (humidity detection)
• Thermoreception (temperature)

Basically, antennae can do everything but see. They play powerfully in orientation of the insect in space; detecting wind speed and direction, the smell of pheromones in the air leading them to a mate, or the subtle vibration of prey below the bark of a tree. What is interesting to me is that antennae have so many different forms. Termites have simple moniliform antennae like tiny strings of tiny beads. Silkmoth and mosquito males have elaborate bipectinate plumose antennae. My small hive beetles have adorable club-shaped antennae which make them look like Mickey Mouse when they hold their antennae up. The antennae of house flies are two fat dangly bulbs with a single feather mounted at the top of each. The antennae of scarab beetles terminate in a fan-like array of delicate fingers called lamellae that can be spread open or closed tightly like a fist and tucked away into cavities under the insect's head. Dragonflies have nothing but two short bristles for antennae. Dizzying variety is the rule when it comes to antennal form. So why so many types? Does each of them correspond to some special life-style like insect leg types?


Question of the day:

Why are there so many types of insect antennae?

Answer:

Dunno.

No, seriously- we don't know why there are so many types of insect antennae. Generally, where olfaction is important, we find more elaborate or specialized antennae, such as those of male moths. Dragonflies, on the other hand, hunt primarily by sight, and thus may be forgiven for having simple and uninteresting antennae. Evolution seems to have favored divergence in most cases and convergence in a few like the elbowed antennae of weevils and ants. Beyond that, antennae are as diverse as the insects themselves. Family resemblance in the antennae is quite useful for classifying insects, but why scarab beetles have fancy lamellate fingers and small hive beetles small club-shaped antennae is rather a mystery.

Some questions in biology will always be easier to answer with "It's for decoration" or "Because that's how God made him." And perhaps in a sense, this is true- that God has seen fit to elevate diversity over uniformity, and style sometimes seems to trump function. But as we scientists study and search for a function for strange traits and find that they do, indeed, have a function, are we disappointed? On the contrary, when fascinating form and amazing function come together we get a new sort of joy- beyond the joy of beauty and the joy of a well-made machine. It is the joy of something that is, on all accounts, very good - just as the creator said it was.