Ant-i-social distancing: Ants know isolation prevents the spread of infection

Originally published on March 13, 2021.

Social distancing was mostly a foreign concept to modern humans until the COVID-19 pandemic hit. It is, however, a behaviour with deep evolutionary roots, practised throughout the animal kingdom.

"We're not the only animals that constantly encounter infectious diseases and so animals have evolved these — to some extent — really elaborate strategies to deal with them," said Sebastien Stockmaier, a postdoctoral student from the University of Texas at Austin.

In a review published in the journal Science, he and his colleagues described how these uncomfortable practices we've adopted to limit the spread of the coronavirus — such as self-isolation, quarantining and social distancing — are especially common in social species like ants.

"Ants are extremely altruistic, so they want all ants in a colony to do well," explained Nathalie Stroeymeyt, a senior lecturer at the University of Bristol in the U.K., who contributed to the paper. 

She studies the strategies that common garden ants — formally known as Lasius niger — use to decrease the risk of spreading disease that could decimate a colony where the ants live in extremely close quarters.

Ants caring for other ants

The ants' social structure within the colony itself centres around keeping the queen ant and her larvae, eggs and pupae, and their "nurses" safe deep inside the colony. This helps protect them from any potential pathogen the foraging worker ants might encounter outside of the colony.

"The older ants tend to be foragers, so they leave the nest to go and look for food or to defend their territory, and [are] less valuable to the colony because they're already much older and close to death anyway," Stroeymeyt told Quirks & Quarks host, Bob McDonald. 

If a forager ant comes into contact with the fungal pathogen, like Metarhizium brunneum, they only have about 24 hours to try and remove the spores from the outside of their body.  After that the spores will start to grow and pierce their exoskeleton and start multiplying inside the ant. 

When they approach death, they will go as far away from the colony as they can to be in isolation in an area where they've got no chance of another nest mate finding their body and becoming infected.- Nathalie Stroeymeyt, University of Bristol

Exposed ants will groom to remove the fungal spores before they enter the colony to avoid infecting others, but they get help with this. Healthy ants they may encounter outside or in the colony's outer periphery that will stop and help them — a behaviour Stroeymeyt compares to human caregiving.

"The healthy ant will groom the ones that have been contaminated to physically remove the spores. And at the same time, they're going to apply formic acid on the ant and also chew the spores with this formic acid, so that they will kill the spores," she said.

Caregiving isn't an entirely selfless act because, like humans who get vaccinated, what doesn't kill the ants may make them stronger. 

"If they do catch an infection, it tends to be a low-level infection, so something that's not going to kill them and that, on the contrary, will boost their immune system," added Stroeymeyt. 

Keeping a distance for prevent further spread

Ants will even take further precautions inside the colony to make sure the younger nurse ants and the vital queen don't get exposed.

Stroeymeyt tracked how ants reacted when a potentially infected individual returned to the colony by placing barcode-like QR codes on their backs, which allowed a camera-equipped computer to track their movements. 

"When some ants become exposed by the pathogen — among the healthy ones inside the colony, there was an increase in social distancing between the nurses and the foragers," she said.

An extreme version of this occurred if the ants became infected with fungal disease. As they got sick, they would flee the the colony to protect it. 

"When they approach death, they will go as far away from the colony as they can to be in isolation in an area where they've got no chance of another nest mate finding their body and becoming infected," said Stroeymeyt.

Isolating by our own free will

While we've been taught to socially distance during this pandemic, there's actually some evidence that behaviours have evolved in humans and other mammals that predispose us to self-isolation if we're sick.  

"When we're sick, we're lethargic. We're not very active. We stay at home. And that, of course, reduces contact with other people," explained Stockmaier who studies this behaviour in vampire bats.

He said vampire bats are extremely co-operative and form strong relationships with others where they not only share food, but groom each other. 

"What we find is that vampire bats that are sick stop grooming others," said Stockmaier. "This is parallel to what we are doing, to some extent."

Be it ants or vampire bats, the scientists agree that one of the biggest takeaways from the animal world is that prevention — something the ants are very good at — is key.

"And that's why we very rarely see an ant colony that is sick in the wild," said Stroeymeyt.

Produced and written by Sonya Buyting.