749. Tending a Sick Comrade Has Benefits for Ants

Ants licking an infected member of the colony

By Sindya Bhanoo, The New York Times, April 9, 2012

When one ant in a colony has an infection, the others don’t avoid their sick comrade. Instead, they approach the infected ant and lick it to remove pathogens.

Now, a new study reports that this works in the benefit of the licking ant as well. By grooming a diseased ant, the helper ant gets a low-level infection that seems to induce the expression of a set of immune genes that help the ants fight off the pathogen.

“At these low levels, their immune system is rather stimulated,” said an author of the study, Sylvia Cremer, an evolutionary biologist at the Institute for Science and Technology in Austria.

She and her team published their findings in the journal PLoS Biology.

The researchers found that only about 2 percent of an infected ant’s nestmates died from the pathogen after licking the diseased one, while more than 60 percent had the benefit of a stimulated immune system.

The ants were gathered from colonies of European garden ants. The researchers applied special fluorescent fungal spores to some ants, and studied their interaction with their nestmates over two days.

The ants’ behavior resembles an old pattern among humans in Africa, in which the scabs of a smallpox victim were rubbed into an open cut on a healthy person as a form of immunization. (Today, vaccines use dead or inactive strains of a virus.) Although the recipient had a 2 percent chance of dying, smallpox mortality fell to about 25 percent.