Abiding by global shelter-in-place orders can be hard for social animals like us, even when we know it’s a matter of life and death.
There are, of course, the countless logistical problems that come with avoiding human contact, but it’s also just lonely for a species that evolved to live with others.
But while social distancing might feel like the most unnatural thing in the world, the sacrifices we’re now making have deep roots in the natural world.
Decades of research has shown that several social species will expel members from their community if they’re infected with a pathogen. Or when an infected animal gets too close, other animals have learnt to stay away.
From ants and lobsters to mice, tadpoles and apes, an array of social animals change their behaviour to reduce the risk of spreading infections.
While studying chimpanzees in Tanzania during the ’60s, renowned primatologist Jane Goodall observed a chimpanzee (Pan troglodytes) named McGregor who’d contracted polio, a highly contagious virus.
His fellow chimps attacked him and cast him out of the troop, according to a report later published in 1986. In one instance, Goodall witnessed the partially paralysed chimp approaching other chimps grooming one another in a tree. Starved of social contact, he reached out a hand in greeting, but the others moved away without a backward glance.
“For a full two minutes old [McGregor] sat motionless, staring after them,” Goodall notes in her 1971 book In the Shadow of Man.
Goodall recorded other instances of ostracised, polio-ridden chimps during her research, reports National Geographic, though noted that in some cases, infected individuals were eventually welcomed back into the group.
Chimps, like humans, are visual creatures, and research suggests that the stigma toward polio-infected chimps might be driven by fear and disgust of their disfigurement. A study published in 2011 suggested that rather than being discriminatory, such stigmatisation could be the strategy for avoiding catching the disease that causes such deformities.
Not all animals are so aggressive toward their ailing neighbours. Sometimes it’s as simple as avoiding those who might infect you.
Scientists have shown than when exposed to a sick tadpole, the healthy tadpoles of the American bullfrog (Lithobates catesbeianus) will do their best to stay away.
Joseph Kiesecker, lead scientist at The Nature Conservancy’s conservation lands team, worked on a study that showed these tadpoles are excellent at social distancing.
In the experiment, Kiesecker placed a tadpole infected with a pathogen around other healthy tadpoles. The tadpoles could smell the chemicals from the sick tadpole. Detecting it was infected, the healthy ones stayed away, according to Kiesecker’s findings.
“It was clear they were using behaviour when given the choice to be near an infected individual, they avoided that infected individual,” he said.
During part of the study, Kiesecker also tested how healthy tadpoles responded to being in close confines with an infected one.
“When we forced them to stay in close proximity and then observed whether they were infected or not, the probability that they’d get infected increased based on the proximity that they were to the infected individual,” Kiesecker said.
Research shows that black garden ants (Lasius niger) also practice social-distancing behaviours when an infected ant is introduced to a group of healthy ones.
A team of researchers at the school of biological sciences at the University of Bristol in England observed how the behaviour of ants changed when those with a fungal disease were introduced to a healthy colony.
After observing the colonies once the infected ants were introduced, the study found that unexposed ants stayed away from the exposed ants and the healthy ones stayed further away from one another as well.
What’s more, the study showed that healthy ants “close rank” around the most vulnerable colony members – the queens and nurses – by keeping them isolated from the foragers that are most likely to introduce germs from outside.
“We believe this is a proactive measure to decrease the risk of epidemic transmission through the colony, not unlike the form of proactive social distancing implemented in our societies to decrease the risk of transmission of Covid-19,” said Nathalie Stroeymeyt, a lecturer at the university.
Even lobsters – highly-socialised creatures who find safety together in sponges, corals or rocky crevices along the ocean floor – have also showed patterns of disease avoidance.
Donald Behringer, a professor of marine and disease ecology at the University of Florida in the US, worked on a study that showed that healthy Caribbean spiny lobsters (Panulirus argus) socially distance themselves from sick ones.
“Healthy lobsters are able to detect and avoid diseased lobsters using chemical cues in the urine of the infected lobsters,” Behringer said. “They don’t even need to see the infected lobster to know they should avoid it.”
The team of researchers placed several lobsters in aquarium tanks, allowing healthy crustaceans to choose an empty artificial den or one occupied by either a healthy or a diseased compatriot.
Unhealthy lobsters didn’t change their behaviour, Behringer explained.
“The sick lobster followed the healthy lobster into a cave and the healthy lobster would be the one to leave,” he said. “Once the healthy lobster left, the unhealthy lobster followed, and it became a game of ‘lobster musical chairs’ until the sun came up and one lobster claimed the cave for the day.”
In most social species, researchers have witnessed animals taking drastic measures to avoid an infected member. But in house mice (Mus musculus) the opposite also happens, at least in some cases.
In 2016 researchers examined how a disease outbreak might affect the social dynamics of house mice living in a barn in Switzerland.
For the study, mice were injected with lipopolysaccharides to simulate an infection and make them feel sick and the mice were also identified and tracked with radio tags, letting the researchers learn how both sick and healthy mice responded.
Although mice have the ability to detect illness in other mice, researchers were surprised to find that healthy mice weren’t avoiding the sick ones, instead interacting with them as if nothing were different.
“It was the sick mouse that removed itself from the group,” lead author Patricia Lopes, a biologist at the University of Zurich, said in a statement.
Researchers explained that the behavioural change might not be intentional. Perhaps the sick mouse just felt lethargic and couldn’t interact the way it normally would. But it could still be evolutionarily adaptive, since self-isolation would help protect the sick mouse’s relatives from the infection.