by Joseph DeSisto
Today saw the description of two new species of South American flies, both fire ant parasites that decapitate their victims. The two new species were discovered in Brazil and Argentina, associated with fire ant mounds in their native territory (Plowes et al. 2015).
Ant-decapitating flies, as might be expected, have unusual and macabre life histories. The adults are tiny, just a few millimeters in length, with the general appearance of fruit flies. Instead of hovering around rotten bananas, however, female ant-decapitating flies hang around ant mounds. When the time is right, a fly soars down to meet her victim, using a hooked, needle-like ovipositor to inject an egg into the ant’s head (Porter 1998).
With egg laid, her work is done. The fly departs, ant still intact and seemingly healthy.
Not all is well, however. From the fly’s egg emerges a maggot that, as it grows, eats away at the inside of the ant’s head. At the same time, the maggot secretes chemicals that cause the ant to go mad, fleeing its colony and finding shelter in moist leaf litter. With its host almost spent, the maggot severs the ant’s head, and forms a cocoon or pupa inside the now-hollow shell. Some weeks later, a new fly emerges and takes off in search of a new ant for her offspring.
This all sounds very sinister, but it also could be very useful to humans. As it happens, many of these flies specialize in decapitating fire ants and, in enough numbers, can seriously impact fire ant colonies. Now that invasive fire ants are well-established in the southern U.S., the Department of Agriculture is looking to ant-decapitating flies to control the ants’ march north.
Whether the two new species of ant-decapitating fly will be useful in controlling fire ants remains to be seen. Multiple fly species have already been introduced in states like Texas (Gilbert and Patrock 2002) and Alabama (Porter et al. 2011), where fire ants are a serious problem for agriculture and human health. In these states the flies have become established and already have a tangible impact on fire ant populations.
However, not all species fare equally well. In order to be useful in controlling fire ants, the flies must be able to adapt to the southern U.S. climate, as well as all the new predators they may not have faced in South America.
Plowes and colleagues (2015) suggest that many more unknown species of ant-decapitators live in remote regions of South America. Discovering new species may help scientists figure out which flies will be most successful at colonizing the U.S., and which species will have the biggest impact on fire ant populations.
Gilbert L.E. and R.J.W. Patrock. 2002. Phorid flies for the biological suppression of imported fire ant in Texas: region specific challenges, recent advances and future prospects. Southwestern Entomologist Supplement 25: 7-17.
Plowes R.M., P.J. Folgarait, and L.E. Gilbert. 2015. Pseudacteon notocaudatus and Pseudacteon obtusitus (Diptera: Phoridae), two new species of fire ant parasitoids from South America. Zootaxa 4032(2): 215-220.
Porter S.D., L.F. Graham, S.J. Johnson, L.G. Thead, and J.A. Briano. 2011. The large decapitating fly Pseudacteon litoralis (Diptera: Phoridae): successfully established on fire ant populations in Alabama. Florida Entomologist 94(2): 208-213.
Porter S. D. 1998. Biology and behavior of Pseudacteon decapitating flies (Diptera: Phoridae) that parasitize Solenopsis fire ants (Hymenoptera: Formicidae). Florida Entomologist 81(3): 292-309.