Ants Change Their Behavior To Control Disease Epidemics

Lasius niger queen and workers individually marked with flat barcode tags that apparently are not heavy enough to change their behavior. Timothée Brütsch

When an infectious disease is raging through a large population, public health teams struggle to find the best way to contain its spread while allowing society to continue to function. Ants have confronted the same issue for millions of years, and at least one species has worked out a sophisticated response, one we may learn from.

The best way to stop an epidemic is with vaccines, but where this option isn't available it's important to work out how to prevent people who are likely to be sick coming into contact with the most vulnerable. Black garden ants (Lasius niger) are affected by the Metarhizium brunneum fungus, their own equivalent of smallpox. If an infected ant brings the fungus back to the nest it can quickly spread, so the ants have invented a type of vaccination, as well as a sort of collective quarantine.

Professor Sylvia Cremer of the Institute of Science and Technology, Austria, observed what happened when 10 percent of the ants from 11 colonies were exposed to the fungus. Tracking the behaviors of individual ants is a challenge, since they look so alike to human eyes, so Cremer and colleagues attached barcodes to 2,266 ants, a commitment to science we don't even want to think about. The coded ants' movements were then tracked every half a second using infrared cameras.

Ants work in teams, with different roles depending on age and status. Foragers are most at risk of exposure to disease-causing agents. Cremer reports in Science the ants were clearly aware when infection reached the colony, and responded differently to colonies dosed with a harmless control.

“The cliques among ants become even stronger, and contact between cliques is reduced. Foragers interact more with foragers, and nurses more with nurses,” Cremer said in a statement, emphasizing the behavior of non-infected ants also changed in order to reduce the risk of the fungus spreading through the colony.

This behavior slowed the pathogen's spread, and in many cases where spores transferred from infected ants to those that had not been exposed the quantity was too small to make them sick. Instead, the low fungal dose sparked the ants' immune systems, protecting them against more intense exposure.

The behavior meant the queen, young, and nurse ants all received less pathogen than foragers. As a result, nine days after the colony was first exposed, many forager ants died, but all the queens, and most nurses, survived, demonstrating the success of the response.

Notably, the ants' reaction was restrained. They didn't isolate infected foragers entirely, as non-epidemiologist commentators demanded during the 2014 Ebola outbreak. Nor, unsurprisingly, were there any signs of anti-vaxxer ants.

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