Imagine a wasp that is smaller than an amoeba. It seems impossible. How could you make a complete wasp, with wings, legs, eyes and a brain, and have it end up smaller than an amoeba?

Forget about it!

But it does exist. It is one of nature’s great experiments in miniaturization.

“Honey, I’ve shrunk the wasp!”

The parasitic wasps, popularly known as fairy flies, are the smallest multi-cellular animals in the world (http://www.wereyouwondering.com/what-is-the-smallest-animal-in-the-world/). Some Megaphragma fairy flies are only about 100 microns in length, while some Amoeba can be as large as 800 microns.

These wasps are made up of many thousands of incredibly tiny cells. The brain of the adult, although exceptionally small, has about four thousand cells. This seems to be all the neurons you need to accomplish a lot of interesting behavior, including flying, finding hosts to lay your eggs on, and breeding. And, another surprise, many fairy flies are quite good swimmers.

How do you make such miniature cells? A recent report by Alexey Polilov shows that during metamorphosis, as the larva converts to adult, 95% of the brain cells lose their nuclei! So of those four thousand adult brain cells only a few hundred actually have nuclei, and all of those associated things, like genes, that most cells take for granted. So the fairy flies have functioning brains, with thousands of cells, but almost no nuclei!

What a surprising space saving trick. It can work for the fairly fly because it only lives about five days. Cells generally need genes to replace the proteins that naturally turn over with time. But if the time frame is short enough then genes become dispensable.