Ants are able to 'self-medicate' by changing diet when they are unwell in first for insect-kind

Findings of study raise questions over how ants 'know' they are sick

File image: Ants have been proven to 'self-medicate' when sick (AFP/Getty Images)

It appears that ants, usually seen as the ultimate self-sacrificing workers, are also not bad at saving their own skins.

Scientists have shown that ants with a life-threatening fungus are able to "self-medicate", eating a normally harmful substance that treats the condition.

This form of "self-medication" in insects has been suspected in research circles but has never been proven until now, raising questions about how the ant "knows" it is sick.

Researchers at the University of Helsinki in Finland showed that ants infected with the fungus Beauveria bassiana would choose to eat small doses of hydrogen peroxide, which had been proven to reduce their deaths by at least 15 per cent.

The fact that most healthy ants gave the poison a wide berth - since it usually caused a 20 per cent mortality rate - appeared to show that sick ants knew the poison would help them recover.

Depending on how strong the toxic solution was, the infected ants would also either choose to eat the poison as often as normal food, or only a quarter of the time, showing they were "careful" about their selecting their doses.

Nick Bos, one of the researchers, said ants close to death in the wild also seem to know because they often leave the nest to die in isolation.

"It is not known yet how ants know they are infected, but it's very clear that they do somehow change their behaviour once they are," he told the New Scientist.

Jessica Abbott of Lund University in Sweden, said the study stood up to scientific scrutiny.

"I think this is good evidence of self-medication," she told the New Scientist. "They showed that the ants deliberately ingest hydrogen peroxide when infected - and that doing so increases the survival of the ant and decreases the fitness of the parasite."

The chemicals found in hydrogen peroxide are also present in aphids and decaying dead ants, leading the Finnish team to say ants in the wild may eat these to fight off infection.

David Baracchi of Queen University of London said that social insects in large colonies like ants and bees are vulnerable to disease, and a small percentage increase in survival rates against infection could make a huge difference to a colony.

"It is natural that they have evolved amazing mechanisms to counteract microorganisms, and self-medication is one of those," said Baracchi. He added it may be a widespread ability in the animal kingdom (a similar phenomenon has already been found in sheep).