Smallest Wasp Is Smaller Than An Amoeba
Big, Small, Tiny
There are more than 600,000 species of wasps in the world. One, called the tarantula hawk (see Image 1), grows to more than two inches long (not counting its legs). It kills tarantula spiders and drags them off to her nest where she then lays a single egg in the carcass.
The species mymar dimidiatus (see Image 2), a member of the wasp family commonly called fairyflies or fairy wasps, averages only one millimeter (mm) in length. There are about 25 millimeters (mm) to the inch. Depending on your browser's font size, the fairy wasp is probably shorter than this dash: -.
Then there is the wasp with the grandiose name megaphragma mymaripenne. It has no common name so, for the purpose of this article (and an ironic twist), it will be referred to as mega. Mega averages five times smaller than dimidiatus at 200 µm (micrometers), or 1/5 of a millimeter, just twice the width of the average human hair. This wasp is smaller than a single-celled amoeba. Unfortunately, there are no public domain images of mega, so you will have to click on this link to appreciate the astonishing size of this insect, scaled into comparison with an amoeba and a parmecium. When I first saw this image, I was skeptical that such a wasp existed, but it's real all right.
Miracle of miniaturization
So how does a fully functioning insect, with wings, eyes, legs, a brain, muscles, a reproductive system, etc manage to be the size, say, of your average single-celled paramecium? Obviously, mega's thousands of individual cells are much smaller than a paramecium or an amoeba, which happen to be among the largest unicellular organisms in nature, but there is a limit to just how small a cell can be.
Russian scientist Alexey Polilov of Lomonosov Moscow State University thinks he's found the answer to this miracle of miniaturization. He discovered that most of the cells in its central nervous system do not have nuclei. An adult wasp has approximately 7,400 neurons (a housefly has 340,000), which is just enough to allow it to fly, feed, locate hosts and lay eggs. Of those 7,400, only about 350 have nuclei. A cell without a nucleus can be considerably smaller than a comparable cell with a nucleus.
Pupa To Adult To Egg To Pupa
To grow, however, neurons must have a nucleus. The nucleus, among other things, provides necessary proteins for the cell to function. Polilov found that, at the beginning, pupal stage, all of mega's neurons contain nuclei, but when they transition to adults, 95% of the nuclei are destroyed and the neurons take up less space. This loss doesn't seem to affect the functioning of the neurons, so Polilov postulates that proteins are stored when the wasp is a pupa and last long enough to allow the adult to exist up to five days, which is a decent age for such a tiny creature.
Megaphragma mymaripenne wasps seek out thrips in order to lay their own eggs inside the thrips' eggs. Thrips are garden pests that average one mm is size, so thrips eggs are pretty tiny, but of course not so small to mega. When the mega eggs hatch inside the thrips' egg, they feed on their unsuspecting host. Since these microscopic wasps are very particular about their target hosts, researchers are looking into ways to use them to control outbreaks of thrips swarms without harming other insects of use to gardeners and farmers.