Ants inoculate themselves by licking sick nest-mates

IF ONE of your neighbours had a life-threatening skin disease, your first response probably wouldn't be to lick them. That's because you are not a social insect. Ants in a colony lick their infected nest-mates, and doing so seems to inoculate them against future infection, protecting the colony.

Sylvia Cremer at the Institute of Science and Technology Austria in Klosterneuburg and colleagues exposed ants (Lasius neglectus) to an infectious fungus called Metarhizium anisopliae. The team then housed each infected ant with five uninfected fellows and watched what happened next.

The healthy ants groomed their infected nest-mates, licking the fungus off them (shown above). As a result they picked up slight infections themselves, although not enough to kill them. Afterwards, two immune-system genes specifically used to fight fungi became activated in the healthy nest-mates, which were then more able to beat the fungus. These effects were not seen in ants that could not touch their infected nest-mates, so the changes were not due to a social signal, such as a pheromone (PLoS Biology, DOI: 10.1371/journal.pbio.1001300).

Cremer thinks the ants were inoculating themselves against the fungal disease, just as humans once inoculated themselves with low levels of smallpox to prepare themselves for full-scale infections.

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