Contaminated Ants Take 'Sick Days' to Protect Colony

Scientists believe ants change their behavior—and have the insect equivalent of taking a day off sick—when they are exposed to pathogens, in order to protect the colony.

The research, published in the journal Science, is believed to be the first to show that the animals can change their behavior to stem the spread of infectious diseases in their densely populated, close-knit communities.

Ants must perform a balancing act of communicating with one another while preventing diseases from passing on in order for their societies to function, the authors of the paper explained.

These societies are complex, with insects falling into different groups depending on their age and roles. Young nurse ants care for infants, while older worker ants venture outside the nest to gather food. It is these worker ants that are most likely to introduce disease into the colony.

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The researchers set out to test whether the presence of a pathogen (in this case a fungus) in the social network affected how black ants behaved.

To do so, they tagged tens of thousands of ants in 22 colonies, and used infrared cameras to study their movements. A 10 percent sample of the colony was then exposed to a fungus. The team watched closely to see if their actions subsequently changed.

They found that ants behaved prophylactically, or in a flexible manner in order to protect their colony from disease—particularly the important queen and nurses.

Sylvia Cremer of the Institute of Science and Technology Austria (IST Austria) explained in a statement: "The ants change how they interact and who they interact with".

"The cliques among ants become even stronger, and contact between cliques is reduced. Foragers interact more with foragers, and nurses more with nurses. This is a response by the whole colony—animals who are not themselves treated with spores also change their behavior."

What's more, this created a process akin to vaccinations among humans.

Nathalie Stroeymeyt, first author of the study and postdoctoral student in Keller's group, told Newsweek: "A surprising result was that the changes in social networks triggered when the ants detect the pathogen not only decrease the risk that the nurses and queen receive a high, potentially mortal pathogen dose, but also increase their chance of receiving a low pathogen dose, which does not cause mortality but leads to immunization (i.e. protection against secondary exposure to the same pathogen, which can be compared to the process of vaccination in humans)."

The study wasn't able to answer whether sick ants stop working for the sake of their nest-mates, Stroeymeyt explained, as the tracking system recorded the location and orientation of the ants, not their detailed behavior.

But an ant isolating itself "would be comparable to taking a day off work in the sense that they decreased their contacts with contaminated co-workers," she argued.

So, can us humans—who are sometimes guilty of a reluctance to go to work when they are sick—learn anything from these clever ants?

Dr. Laurent Keller, Professor of Evolutionary Ecology at the University of Lausanne, told Newsweek: "Indeed it probably makes biological (and economical?) sense for people who suffer from an infectious disease to remain at home until they are no longer infectious, rather than coming to work and contaminate their co-workers."