An ancient war has arrived in the southern USA. The mortal enemies have, over their long bloody history, each developed a sophisticated arsenal of chemical weapons for annihilating the other. The combatants are two species of ant – the imported fire ant Solenopsis invicta and the tawny crazy ant, Nylanderia fulva. A recent article in Science reports that in addition to chemical weaponry, it seems that N. fulva also produces a chemical defence.
Solenopsis invicta (originally found in South America) is a highly disruptive invasive species in the southern USA where it displaces native ant species through its ability to produce a potent insecticide. However, in recent years, N. fulva (from the same geographical area as S. invicta) has invaded S. invicta's US territory, even building nests inside S. invicta ant mounds. Postdoctoral fellow Edward LeBrun and his co-authors Nathan Jones and Lawrence Gilbert at the University of Texas at Austin wondered why N. fulva doesn't avoid S. invicta like other ant species do.
LeBrun and his colleagues describe how N. fulva charges large groups of S. invicta during combat, spraying venom, while S. invicta fires back with its own venom. The authors observed that after being sprayed with venom, N. fulva workers smear a secretion on their mandibles, run their front legs through their mandibles, and then groom themselves with their front legs. This suggested to LeBrun and colleagues that N. fulva might be able to detoxify S. invicta's usually deadly venom.
To test whether the secretion could help N. fulva survive S. invicta's venom, LeBrun and his co-authors sealed the opening to the exocrine glands that produce N. fulva's secretions with nail polish in some individuals and kept it unsealed in others. They found that N. fulva with unsealed glands easily survived encounters with S. invicta, while N. fulva with sealed glands usually died within 8 h.
Next, as N. fulva has two different exocrine glands (the Dufour's gland and the venom gland) that exit the same pore, the authors wanted to know which gland produced the detoxifying agent and what that agent might be. They found that N. fulva survived S. invicta venom easily when smeared with their own venom gland secretion but not the Dufour's gland secretion. As N. fulva venom is mostly made of formic acid, the authors then showed that formic acid protected these ants from S. invicta venom.
Finally, the authors tested whether N. fulva reacted with their washing behaviour in response to most ant species, or reserved it for S. invicta attacks by staging battles where they pitted several species of ant against N. fulva. They found that although N. fulva washed after battles with any ant species, they spent the most effort detoxifying after encountering S. invicta.
The two ant species have a long evolutionary history together in their South American home, while sharing battlegrounds with other ant species that control both populations. However, given there are no other species around to keep them in check in the southern USA, understanding how N. fulva neutralises S. invicta venom could help humans learn to manage both species.