We're all (unfortunately) familiar with the red imported fire ants that have become so prolific in lawns across the southern United States. These were introduced from South America early last century through our own Mobile, Alabama on cargo ships. We might not be aware of the billions of dollars these ants cost anually in agricultural damage, pest control costs, and hospital bills from treating their painful and even potentially deadly stings. Still less familiar to most people are one of the fire ants' natural enemies, the phorid flies, otherwise known as ant-decapitating flies.
These flies, also native to South America, belong to the genus Pseudacteon, and are parasitoids of fire ants. Unlike true parasites which depend on their hosts for survival, parasitoids eventually sterilize or kill their hosts. As the name ant-decapitating fly suggests, the host insect's death might be seem as brutal.
Female phorid flies, in an ironic twist, are attracted by the smell of the ants' alarm pheromones, a chemical substance which the ants themselves release to warn their fellow ants of impending danger. Once she has a target in site, the female fly deposits an egg inside the ant's thorax. The egg then hatches and the newly hatched larvae migrates to the ant's head, where it feeds on its host's bodily fluids and later its brain.
Eventually, the fly larvae releases an enzyme which causes the ant's head to fall off. The fly larvae completes its development within the decapitated ant head, until it emerges like something out of a horror movie and begins the process anew. ..............................
Alabama is home to dozens of species of native phorid flies, most of which are believed to be parasitoids of other insect species. This includes phorid flies in the genus Apocephalus, which are parasitoids of our native carpenter ants, and which grow much larger than their tropical cousins. This is because the host carpenter ants themselves are much larger (and have much larger heads) than fire ants, meaning a larger food source for larger flies.
Since we have these ant-decapitating flies right here in the United States, you may be wondering why we still have so many fire ants around. That's because these phorid flies are very host-specific in their feeding. The native phorid flies here in the US attack native ant species, but very rarely touch imported ant species. As is often the case with imported (and many times invasive) organisms, we need to also import the accompanying parasitoids and other pests that keep their populations low in their native homeland.
The good news is, pest control companies and entomologists alike are doing just that. Since 1997, South American phorid flies have been introduced across the Southeast, from Texas to Mobile. Preliminary results from these introductions point to a 10 to 20 percent drop in invasive fire ant populations.
Look forward to many decapitated fire ants coming soon to a lawn near you!
Mitchell Vaughan, Auburn University Department or Horticulture and Extension Graduate Student, Fall 2016
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