Healthy ants typically avoid harmful substances called reactive oxygen species, such as peroxides. But when they’re infected by a fungus, selectively ingesting those molecules will actually help them survive. The findings, published in Evolution this week, show that ants know how to fight diseases by medicating themselves.
While not necessarily recommended, self-medication – or actively consuming biologically active compounds – can sometimes help prevent, clear, or alleviate symptoms of disease. That’s likely the case for social insects living in dense, humid colonies where their genetic diversity is low and they’re especially vulnerable to parasites. However, there’s been no conclusive evidence for this behavior, until now.
A University of Helsinki team led by Nick Bos found that when Formica fusca ants are exposed to a fungal pathogen called Beauveria bassiana, they’ll deliberately consume harmful reactive oxygen species (ROS). This is the first time something like this has been documented.
Healthy ants fed a honey-based diet laced with hydrogen peroxide suffered a mortality rate of about 20%. While this increased ROS uptake is clearly costly for uninfected ants, it results in higher survival for exposed ants. Fungus-infected ants eating an ordinary honey-based diet showed a death rate of about 60%, New Scientist reports, while the death toll of infected ants given food spiked with hydrogen peroxide was 45%. And those infected ants chose their dosage carefully too.
“It is not known yet how ants know they are infected, but it’s very clear that they do somehow change their behavior once they are,” Bos says. Some ants close to death will leave the nest to die in isolation, he adds, so they must somehow know they’re ill. Hydrogen peroxide is a good source of ROS in the lab, and the team suspects that in the wild, ants ingest ROS by eating aphids or decaying plant matter.