A new species of phorid fly from Thailand is the smallest fly ever discovered. At just 0.40 millimeters in length, it is 15 times smaller than a house fly and five times smaller than a fruit fly.

The tiny fly, Euryplatea nanaknihali, is also the first of its genus to be discovered in Asia, and it belongs to a fly family (Phoridae) that is known for "decapitating" ants.

Some species in the Phoridae fly family lay eggs in the bodies of ants, and the resulting larvae feed in the ants' heads, eventually causing decapitation. In fact, some of these phorid flies are being used to try to control fire ants in the southern United Sates.

According to Dr. Brian Brown of the Natural History Museum of Los Angeles County, these flies can probably decapitate some of the smallest ants in the world, ones with heads as small as 0.5 millimeters. Although this has not yet been observed, it is highly likely because the fly's only known relative, Euryplatea eidmanni, is known to parasitize ants in Equatorial Guinea.

"It had always been assumed that smaller species of ants would be free from attack because it would be physically impossible for flies that are 1-3 millimeters in length to develop in their relatively tiny heads," he said.

"However, here we show that even the smallest host ants in a host-parasitoid system cannot escape parasitism."

The new fly species is described in the July issue of Annals of the Entomological Society of America in an article called "Small Size No Protection for Acrobat Ants: World's Smallest Fly Is a Parasitic Phorid (Diptera: Phoridae)".