Monday, November 8, 2010

The Potter Wasp

We have just learned about a beautiful little insect called the potter wasp (the picture of the pot to the left is from Wikimedia Commons) from the Nov 10 episode of the BBC Radio 4 program, Living World.  There are 6500 species of wasp in the UK, but this is a solitary and rather elusive wasp that lives on the southern edge of the isles, but they can also be found in Europe, east to Asia and west to North America.  We've come late to this discovery, and to blogging about it -- here are some additional lovely pictures of the pots these wasps construct.

The adult female lives for about 6 weeks in the summer, during which time she constructs 15 or 20 little pots, each maybe 1 centimeter tall and made of clay that she mixes from earth from a carefully chosen "quarry" and her own saliva.  She'll fly 60 meters or more from the quarry to construct her pots, often in a bush, but if she's near a town, she might make them on roofs or other such 'unnatural' places.

Each pot takes a few hours to complete.  When it's finished, the wasp lays a single egg inside, and then proceeds to provision it.  She hunts for tiny caterpillars, which she paralyzes and stuffs into the pot until there's no room for any more. She then seals the pot and flies off to make another.  The larva hatches in a few weeks, consumes the caterpillars, and makes itself a cocoon in which it overwinters.  When the weather is warm enough, the insect eats its way out of the pot and goes on to live the short life of an adult potter wasp.

Now, this is very interesting indeed.  No wasp is taught to make these pots, nor are the larva taught to make their cocoons, nor to eat their way out of their first homes to out into the world to perpetuate the cycle.  This is clearly genetically driven behavior, and complex behavior at that.  

And these wasps aren't automatons.  They apparently leave a distinctive signature on their pots, some building all slanted pots, some all upright, and so on.  And they spend time choosing the spot of the quarry from which they'll construct their pots, assessing the soil and deciding where it's just right, and then choosing where to locate their pots.  And, if they've laid an egg and then the weather turns, or the temperature drops, or they can't find caterpillars and the egg dies, they recognize this and don't then fill the pot with food.  

Clearly complex behavior, and apparently with some decision making going on.  There may -- must -- be a lot 'hard-wiring' involved.  But how can this work?  How do these wasps know what to do from day one, and with no instruction when clearly decisions must be based on their local experiences?  And why do we here at MT continually criticize what we think are too-easy assertions that human behavior is genetically determined?  

Synapses in human brains apparently are laid down in response to experience.  How do insect brains develop?  The standard Darwinian answer is important, and it is not new, and the problem (through other examples) was well-known to Darwin.

The standard explanation is that the trait evolves by natural selection.  The wasp doesn't have to 'know' in any conscious sense what it's doing.  It suffices that gradually, wasps who performed earlier more primitive versions of this behavior reproduced better than wasps who didn't.  Over time what was once a rudimentary version, became today's highly sophisticated version.  The Darwinian explanation is really a statement of assumption that this kind of process is responsible -- and we tend to accept such explanations with the idea that someday neurobiology will be able to work out the mechanisms in today's wasps by which we can develop more genetically specific explanations.

That's a major axiom to make such a blanket application of Darwin's masterful idea.  Of course, this is just the kind of trait that Intelligent Design advocates like to point to as proof that Darwin was wrong.  Evolutionary biologists invoke natural selection because there is so much evidence that the general idea was cogent, and also because we simply have no better kind of explanation (and instant creation is no explanation at all).  But history shows that science will make progress in understanding these wasps' talents. Perhaps wasp experts will be able to point to 'intermediate' states of this kind of behavior in other closely related wasp species.  Even if that shows that gradual evolution of such a trait could occur, it doesn't explain the neural mechanism, which must be very interesting indeed.

Darwin himself marveled at insect behavior.  In Descent of Man, 1871, he wrote:
...the wonderfully diversified instincts, mental powers, and affections of ants are notorious, yet their cerebral ganglia are not so large as the quarter of a small pin’s head. Under this view, the brain of an ant is one of the most marvelous atoms of matter in the world, perhaps more so than the brain of a man.
For all the reasons of the nature of complexity, that are so easy to observe in so many traits, and that we write about a lot, it is a challenge to accept the standard explanations without wondering if  there may not be something about these processes that science simply has not yet discovered.  But if that is or at least should be a nagging concern even for many biologists, one of the other pervasive and humbling facts that we must  keep in mind is that humans have a difficult time getting our heads around the notion of what can happen in millions of generations.  It is to a great extent today, as it was to Darwin, the major challenge to understanding the workings of evolution.


James Goetz said...

Absolutely fascinating. What's more fascinating is imagining how 6500 species of wasps journeyed from Noah's Ark to the UK.:) Or wait, how would intelligent design try to explain the UK's 6500 species of wasps including the potter wasp?

Anne Buchanan said...

Ha! I'm sure someone has that figured out, Jim!

GGreene said...

Isn't it obvious? The instructions are on the *inside* of the pot, written in Wasp, of course, which to us just looks like the interior surface of a potter wasp pot. ;-)

James Goetz said...

Well, GGreene, that doesn't explain the genetically driven behavior of reading and writing wasp.:)

Holly Dunsworth said...

Where can I sign up to be a potter wasp archaeologist?
(This is absolutely awesome, btw.)

Unknown said...

Very interesting article, I had a wasp on one of my patio flowers last week, wasn't sure why she was so interested in that particular flower but Monday morning I found a tiny little nest which I was able to identify as the potter wasps nest. It looks like a miniature work of art, nature never fails to amaze.