I don’t consider myself a “geek” (indeed, I hate that word, since it’s basically anti-science), but I have to admit that the publication of this paper, which I learned about from Brian Brown—one of its authors who posted about it on his website, flyobsession—got my juices flowing a bit faster. In a paper in the Annals of the Entomological Society of America (reference below), Brown describes the world’s smallest fly, a phorid.
Phroids are weird flies (I’ve posted about them twice, here and here): often parasitic, tiny, and wingless, and assuming bizarre forms. The picture below, taken from Brown’s paper, shows some other phorids, and check out my two posts in the last sentence. Remember, these are adult flies!:
One female specimen of the new species, named Euryplatea nanaknihali, was found in Thailand. This is what it looks like (like many phorids, its wings are tiny); the photo is from Brown’s website:
Of all the contenders for the title of world’s smallest species of fly, it seems that a species of Phoridae described here is the champion. At a body length of 0.40 mm, it is smaller than all of the tiny gnats, mosquitoes, and other flies so far described.
Four-tenths of a millimeter is 0.016 inch. In other words, you’d have to line up 63 of these little guys to make an inch. Here’s a line that is about 1 mm long, so the fly is less than half this size:
Here’s how big it is compared to a housefly (Musca domestica); the figure is again from Brown’s paper:
Although only one specimen was found, Brown hypothesizes, almost certainly correctly, that this is parasitic on small ants. Brown’s website notes:
The smallest fly in the world is a member of the family Phoridae, and is one of the “ant decapitating flies”. Adult females lay an egg in the body of an ant, and the resulting larva feeds in the ants head, eventually causing the decapitation of its host. Some of these flies are being used to attempt biological control on imported fire ants, and were even featured on an episode of the popular television show “King of the Hill”.
Because these flies usually develop in the head of their host ant, they are smaller than their hosts. One would think that the smallest ants would be therefore immune to these nasty parasites, as their heads are vanishingly small. But the world’s smallest fly is one of these ant killers, and at the astoundingly small body length of 0.4 mm, these flies can probably decapitate ants with heads as small as 0.5 mm. That is pretty close to the smallest size that ants can get!
So is this the world’s smallest insect? Nope. According to Brown’s paper, “the smallest known insects are reputedly mymarids that are only ≈0.14 mm in length, also making them the smallest animals in the world.” That’s a third the size of this fly, and 0.0055 inches long (you’d have to line up 182 of them to encompass an inch). Mymarids, which are minute wasps, are so small because they parasitize the eggs of other insects. And within these flies, and those wasps, are tiny, tiny brains that have enough information to control their complex behaviors.
Ain’t nature wonderful?
Brown, B.V. 2012. Small size no protection for acrobat ants: world’s smallest fly Is a parasitic pphorid (Diptera: Phoridae). Ann. Entomol. Soc. Am. 105(4): 550-554.