A Baffling Mystery: These Ants Decorate Their Nests with Enemy Skulls

ANTS IN FLORIDA COLLECT THE SKULLS OF OTHER ANTS TO DECORATE THEIR NESTS

Original source: https://www.newsweek.com/florida-ants-skulls-trap-jaw-ant-predator-nature-acid-spray-1217323?ICID=ref_fark&fbclid=IwAR3_Smn5Y3C9ix7-2xfLtfcJnEnFURbksBsCge0VTukYtv1vnF08XgdnVGQ

Chinese translation: https://www.natgeomedia.com/news/ngnews/86137?fbclid=IwAR2bbhKzCHwSlipn7MWS-PMzCq1ZBhj0k5Wva2SqxAwYbFEFlqOesy8oSQc

Formica archboldi is a species of the genus Formica found in Florida. It has been studied locally for more than 60 years, and from the start, researchers noticed that its nests were often littered with the remains of trap-jaw ants (Odontomachus), especially their heads.

The original assumption was that this Formica species took over trap-jaw ant nests, but after much longer study it turned out that this was not the case at all!

In fact, this Formica species preys on trap-jaw ants. Hard to believe… (Trap-jaw ants are formidable predators with spring-loaded mandibles that snap shut on prey via a nerve reflex. The sheer speed and force of that snap, combined with the barbs on the mandibles, leave prey with no chance of escape.)

Ants really are the most amazing creatures in the world. Formica ants have no soldier caste and look nothing like as striking as trap-jaw ants, yet they turn out to be the trap-jaw ant’s predator. Incredible!

Thanks to fellow ant keeper Alan for the following notes: Having read the original paper, it does not specifically say the skulls are kept to better mimic the trap-jaw ants’ scent. The skull-collecting habit may simply be because these ants tend to leave their refuse inside the nest rather than dumping it outside. The paper also ran several experiments and found that (1) Formica archboldi really is better than other Formica (F. pallidefulva) at using formic acid to paralyze trap-jaw ants. (2) The cuticular hydrocarbons of Formica archboldi really are highly similar to those of the trap-jaw ants living nearby, and this is tied to locality: ants from different regions are not similar. But it also found that (3) Formica archboldi shows no preference for hunting trap-jaw ants with similar cuticular hydrocarbons; it hunts any trap-jaw ant. (4) Trap-jaw ants are no less likely to fight back when the hydrocarbons are similar; there was no significant difference in the rate of counterattack between similar and dissimilar profiles. That raises a puzzle: the cuticular hydrocarbon profile of Formica archboldi matches that of local trap-jaw ants to a degree normally seen in social parasites, yet it does nothing to reduce the trap-jaw ants’ counterattacks. So what is the highly similar hydrocarbon profile actually for? The researchers do not yet have an answer. They did propose an interesting direction for future work: studying the relationship between the local trap-jaw ants and Polyergus oligergus, the slave-making ant that raids Formica archboldi. Perhaps Formica archboldi evolved its closely matching cuticular hydrocarbons not to hunt trap-jaw ants, but to deal with the slave-makers: hunting trap-jaw ants while also disguising itself as one, so the slave-makers leave it alone. That is roughly the gist.