Re: Why do wasp's hind legs hang down while the front 4 are tucked in?

Nathan,

This is not an easy question to answer, mainly because the answer is perhaps somewhat less than exciting.

There are many different species in the Order Hymenoptera (wasps, bees and ants), about 100,000 species and counting. So there are many different kinds of wasps, all of which share a common ancestor, but nevertheless derive from lineages that are quite distinct. Some, such as the vespines (hornets and yellow jackets) in fact do tuck all six legs under when flying, much like a bee. Other wasps though, such as the paper-nest making wasps, the polistines, allow their legs to hang as you suggest.

The uninteresting part of this answer (assuming you found the info thus far interesting) is that there is no particular 'reason' why this is. In biology, we often speak of 'reasons' why certain organisms have certain traits. This is because we believe that the process of natural selection can mold species over time in such a way that they retain traits that help them with specific tasks and lose traits which are not helpful. But this is not always the case. Some traits are retained by species through time and these traits don't really seem to assist the organisms in any particular way (that is, they do not appear to be adaptive). But these traits also do not seem to be costly to the organisms either, so they are not eliminated.

Other biologists believe that certain traits simply cannot be eliminated in all cases by natural selection. Take the following example, keeping in mind that Darwinian natural selection requires that:

1. organisms have variable traits
2. some of these traits are heritable
3. some of the heritable traits will allow the organisms that have them to leave more offspring than organisms with other traits

Let's say there is an initial population of wasps. Some of them hang their legs low while in flight, others don't hang their legs at all. And let's further suppose that wasps that do not hang their legs are better at flight and therefore avoid predators (or crashing into walls, etc.) more easily. In this case, better fliers will leave more offspring, and over time, the population will be composed of only wasps that do not hang their legs. But if the initial population is composed of only wasps that hang their legs, natural selection cannot act on the population because of this lack of variation. Such populations are said to be fixed for the trait. The inability of natural selection to shape a fixed trait is known as phylogenetic inertia.

Wasps' leg-hanging in my view is one of these traits that seems to have no real adaptive value. I'd like to be able to say otherwise, but sometimes the truth is, well, kinda boring.

Keep asking questions, and for further information on the topic of phylogenetic inertia you might check out the following references:

• Gould, S. J. and R. C. Lewontin. 1979. The spandrels of San Marco and the Panglossian paradigm: a critique of the adaptationist programme. Proceedings of the Royal Society of London. B. 205, 581-598.
• Eldredge, N. and J. Cracraft. Phylogenetic Patterns and the Evolutionary Process. Method and Theory in Comparative Biology. Columbia University Press, New York, 1980.