Ant guy Ed LeBrun has a paper out in Science today documenting a novel defensive use for formic acid: detoxifying the venom of competing fire ants:
Abstract: As tawny crazy ants (Nylanderia fulva) invade the southern USA, they often displace imported fire ants (Solenopsis invicta). Following exposure to S. invicta venom, N. fulva applies abdominal exocrine gland secretions to its cuticle. Bioassays reveal that these secretions detoxify S. invicta venom. Further, formic acid, from N. fulva venom, is the detoxifying agent. N. fulva exhibits this detoxification behavior after conflict with a variety of ant species; however, it expresses it most intensely after interactions with S. invicta. This behavior may have evolved in their shared South American native range. The unique capacity to detoxify a major competitor’s venom likely contributes substantially to its ability to displace S. invicta populations, making this behavior a causative agent in the ecological transformation of regional arthropod assemblages.
Normally, formic acid from the ants’ venom gland is applied to an opponent as a potent volatile weapon, but this sort of self-medication is novel. I haven’t read the paper in depth, but it looks fascinating.
I’ve long been interested in the invasion of North America by a suite of highly-competitive species from the same region of Argentina. Some of the most dominant ants in along the gulf coast are imports: fire ants, Argentine ants, tawny crazy ants, Pheidole obscurithorax, and rover ants all know each other, so to speak, from their interactions along the banks of the Paraná river. Thus, this detoxification behavior likely originated long before any of these ants hitchhiked to North America.
Source: LeBrun EG, Jones NT, Gilbert LE (2014) Chemical Warfare Among Invaders: A Detoxification Interaction Facilitates an Ant Invasion. Science, online early. doi: 10.1126/science.1245833