The Palestinian gadfly (Nannospalax ehrenbergi) is a complete introvert. Living just under half a meter underground, it digs its own tunnels where it spends most of its life collecting roots, tubers and bulbs. Each blind has its own territory - and for good reason: if one individual accidentally burrows into the tunnel of another, the rodents bare their teeth or bite each other in fierce, often fatal fights.
Blindfoots usually interact with other members of their species only during mating season, but even then they must proceed with caution. The male swarms through the soil towards the female, but stops before entering her tunnel.
For several days, they send vibration signals to each other by drumming their heads on the surfaces of the tunnel. Only when the female expresses interest in meeting them does the male move forward, mate with her and leave. After closing the tunnel behind him, he continues his reclusive lifestyle.
A study of singles
Solitary lifestyles like this are surprisingly widespread in the animal kingdom. Even among the generally sociable mammals, 22% of the species studied are largely solitary, meaning that males and females spend most of their time sleeping, foraging or hunting alone.
However, scientists pay relatively little attention to solitary animals. Perhaps because humans are social creatures themselves, and humans are more attracted to the study of creatures that group together to defend or search for food, reproduce, and raise offspring.
Experts say that for a long time, many scientists have overlooked solitary life, seeing it as a more primitive, basic form of existence associated with antisocial behavior and low
intelligence.
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But now researchers are coming to realize that some animals evolved to be solitary precisely because it can be useful for escaping the competition and stressful conditions of group life. What's more, many solitary animals are actually very intelligent and live diverse and complex social lives despite their
solitude.
Although
blindfolds are an exception, many solitary animals tolerate, learn from, and sometimes even cooperate with others of their kind, allowing them to enjoy the best of both worlds.
As people increasingly spend time alone, these animals are a reminder of the many benefits of solitude and that living alone doesn't mean you have to be lonely - a thought that might be worth thinking about for people who spend
Valentine's Day alone.
"Perhaps by studying solitary species and how they succeed in this tactic... we will also be able to better define for human society what is good about solitude," says behavioral ecologist Karsten Schradin of the Centre National de la Recherche Scientifique in Strasbourg, France, and co-author of the 2024 survey on mammalian solitary life.
Life in groups
Living in groups certainly has many advantages. Think of zebras, which find safety in herds, and lions, which often hunt together to overpower prey larger and faster than themselves. Some birds raise offspring together, and chimpanzees socialize by picking parasites off each other.
But there are downsides to this. In a group, "every shelter has to be shared, every bit of food has to be shared, every access to the male has to be shared," says David Scheel, a behavioral ecologist at Alaska Pacific University. "Or if the food is not shared, only one of you can have it."
While hunting and sharing food together makes sense for animals such as lions, which are often surrounded by abundant and large prey that can feed several individuals, it is less beneficial in situations where prey is smaller and cannot be shared. It is also not as useful when prey is scattered across the landscape and more effort is required to find it.
This may be why armadillos and anteaters feed alone on rare insects, and why tigers, which roam far and wide in search of relatively scarce prey, hunt singly, which helps them sneak up on their prey more easily. To further reduce competition, tigers and some other solitary hunters "take over" small territories that they defend from other predators.
The pros and cons of being single
For gadflies, solitude means not having to constantly compete for space in a tunnel, which takes a lot of energy to dig. Solitary animals also have less competition for males and less risk of contracting diseases and parasites.
At the same time, females raising young may put all their energy into caring for their own offspring, not caring about neighboring cubs as some more social species do. In other creatures, such as sloths, camouflage may only work if they do not congregate in large groups.
"If you live alone, you are less conspicuous," says Lindelani Mayuka, a zoologist at the University of the Witwatersrand in Johannesburg, South Africa, and co-author of the review with Shradin.
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Living alone also creates problems - such as the lost benefits of sharing the warmth. But some animals, such as the Karoo forest rat (Myotomys unisulcatus) in southern
Africa, get around this problem by building large huts of sticks to protect themselves from temperature extremes and predators.
For very social animals, loneliness can be
stressful, often leading to poor health and anxiety, but solitary animals do just fine. Middle Eastern gadflies, for example, experience stress and anxiety when placed next to each other, even if there is a barrier between them, with smaller, more docile individuals suffering the most.
"They can die from the stress they experience," says Tali Kimchi, a behavioral neurobiologist at the Weizmann Institute in Israel who studies the gadflies in her lab.
Like all mammals, mother gadflies care for their offspring, but they eventually become hostile, forcing the cubs to dig away from their tunnels.
"It sounds funny, but that's the survival of these creatures," she says. Not all solitary species actively repel each other. Many come together through shared resources and lead surprisingly rich social lives, tolerating each other and even cooperating when it makes sense.
For example, Karoo forest rats that live near related individuals interact frequently and amicably with each other - sharing feeding grounds with related females, and sometimes even bonding at the end of the breeding season when they are in high demand.
Octopuses
"The fact that some animals lead solitary lives doesn't mean they don't have social interactions," Mayuka says.
Even some
octopuses - a group once thought to be so solitary that it was joked that they only met to mate or eat each other - sometimes team up.
At one site in Jervis Bay in eastern Australia, individuals of a species called the dingy octopus (Octopus tetricus) congregate together because of the presence of shelter. It probably started when one octopus began accumulating discarded shells after eating, which eventually stabilized the sediment enough for another octopus to build its burrow in the area.
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This new resident then created its own pile of discarded shells - and so on until as many as 16 octopuses had gathered in one spot, says Scheel, who studied the site with his colleagues. In this "octopus city," individuals find themselves in much tighter quarters than they're used to and exhibit curious behavior to cope with others of their kind.
Males sometimes try to persuade females to stick around, chasing other males-sometimes crawling into each other's burrows, wrestling with them, and driving them out. Sometimes, when the expelled males return to their burrow, "the male who expelled them may return and repeat the expulsion," Scheel says.
When cleaning their burrows, octopuses often push leftovers after a meal to the side of their neighbors. Sometimes they hold them and then dump them on each other, says Scheel, who documented some of these interactions in a 2022 paper.
Some scientists call this behavior neither aggressive nor cooperative, but "rivalry," says Scheel, who is still figuring out the purpose of these interactions. "We put a solitary animal in a complex social situation, and all it does is compete with the people around it, and yet it looks perfectly healthy. This suggests that they are either less lonely than we thought, or the stress of the social situation is not that great for them," he says.
Such complex social interactions emphasize the intelligence of solitary creatures.
Reptiles
Similarly, researchers have observed how some solitary reptiles closely monitor other individuals and use that information to solve problems - an ability previously thought to be unique to humans, says behavioral scientist Anna Wilkinson of the University of Lincoln, UK.
"Animals that may not be able to naturally form complex groups actually have very complex aspects of social learning," she says.
For example, in experiments with coal turtles (Chelonoidis carbonarius), which forage alone but can run into each other under fruit-bearing trees, Wilkinson presented them with a V-shaped transparent fence with food inside. Neither animal could reach the food until Wilkinson and her colleagues taught one of them to do so.
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Seeing their mate reach for food, the other turtles immediately followed suit. It is particularly remarkable that reptiles are able to learn from other individuals through imitation, given that many of them hatched from eggs without parents around to teach them these skills.
Perspectives on loneliness
Such evidence leads scientists to view solitary lifestyles not as a fixed, single category, but rather as a continuum: from animals such as the antisocial gadfly to species that live mostly alone but learn from and cooperate with each other.
Some species even combine solitary and more social lifestyles, such as the community-dwelling striped grass mice, which go off alone once they start breeding, or raccoon coati, whose males live alone while females hunt in groups.
Studying solitary animals and their social networks can help conservationists better protect and preserve their populations from human threats.
Mayuka and Shradin have already begun work to create a community of scientists to further study the lives, benefits, needs and challenges of solitary animals. "Solitude is not simple or primitive," says Shradin. "It can be quite complex and create problems ... that are solved in different ways in different species."
Understanding the diversity of the solitary lifestyle can be useful for humans as well. Kimchi studies changes in the brains of blind mice as they switch between introverted and more social stages of mating and raising cubs. Perhaps such research could help us understand how people with neurological or psychiatric illnesses become socially withdrawn.
But solitary animals can also help us understand that loneliness doesn't have to be problematic, even if it is somewhat stigmatized in extrovert-oriented human society. "Social" solitary animals create meaningful social networks around them - and people who live alone can do the same.