What Is a Group of Rats Called?

A group of rats is most commonly called a “mischief.” The term belongs to the long English tradition of fanciful collective nouns, and while you will also hear “colony,” “horde,” “pack,” and “swarm” used in casual speech, “mischief” is the one that appears in most dictionaries and word-reference lists. The name turns out to be oddly fitting: the more researchers study how rats live together, the more complex and surprisingly cooperative their group life appears to be.

Why “Mischief” and When to Use Other Terms

English has hundreds of collective nouns for animal groups, many of them dating to late-medieval hunting manuals and wordplay lists. A “mischief of rats” sits alongside a “murder of crows” and a “parliament of owls” in that tradition. Unlike those better-known examples, “mischief” has stayed relatively obscure, which is why so many people end up searching for it.

In practice, the word you choose depends on what you are describing. “Mischief” works as a general-purpose label for any gathering of rats. “Colony” is what biologists and pest-control professionals tend to use, because it implies a more permanent, structured social unit with shared nesting sites and overlapping home ranges. “Horde” and “swarm” show up mostly in dramatic or informal contexts, often when someone is describing a large number of rats moving together. None of these terms is wrong, but “mischief” is the trivia-night answer, and “colony” is the one you will encounter in scientific literature.

What a Wild Rat Colony Actually Looks Like

The Norway rat, the species behind most of the world’s urban rat problems, is deeply social. Wild colonies can be large. Research on Norway rat social life describes colonies that, depending on food resources, may include more than 150 individuals.¹ These colonies are not unstructured masses of animals. They break down into smaller subgroups: pairs, harems with or without pups, single-sex clusters, and solitary individuals that float between subunits.

Rats in a colony share a burrow system of interconnected tunnels and chambers. Some chambers serve as communal nests, others as food-storage rooms. The whole structure is collectively excavated, meaning members of the group contribute labor to building and maintaining the network.¹ The arrangement is not all that different from a small underground apartment building, with shared hallways and private rooms.

The Pecking Order Inside the Group

Within a colony, rats organize themselves into dominance hierarchies, and these hierarchies are surprisingly stable once they are established. Long-term tracking of laboratory rat groups has found that group social structure stays consistent as long as membership does not change, though some groups go through reshuffling periods where the rank order shifts before settling again.²

Biologists who study Norway rats have identified three broad male types within a colony. Alpha males are typically the largest animals. They move freely, eat first, and lead the charge when an unfamiliar rat wanders in. Beta males give way to the alpha but still manage to maintain their body weight and may reproduce when the opportunity arises. At the bottom sit omega males, who tend to lose weight over time, rarely mate, and often leave the colony entirely to try their luck elsewhere.¹ This dispersal of low-ranking males is one of the main ways new colonies get founded.

Interestingly, rank stability depends partly on social context. Research comparing dominance in group housing versus isolated pairs found that rankings were less stable when rats lived in full groups than when they were tested in pairs. The group setting introduces enough social complexity that positions can shift more readily, for both males and females.³ In other words, having more neighbors creates more politics.

How Rats Know Who Belongs

One of the most striking features of a rat colony is how aggressively its members defend their territory against outsiders. When a strange rat is introduced to an established colony, the dominant males attack. These attacks follow a predictable pattern: bites concentrate on specific body regions, while other areas, like the belly, go virtually untouched. Defenders have counter-strategies: a cornered intruder will rear up on its hind legs in a “boxing” posture or roll onto its back, interposing that protected ventral area between itself and the attacker. The attacker responds with a sideways “lateral display” designed to get around the defense.⁴ This choreography looks almost ritualized, because it essentially is: both sides are working within a set of behavioral rules that limit the risk of fatal injury while still enforcing group boundaries.

Rats distinguish colony members from strangers largely through scent. Mammalian social odors carry layered information, including signals about species, sex, age, individual identity, social rank, and colony membership.⁵ A rat that smells “wrong” gets treated as an intruder. This scent-based recognition system explains why colonies stay cohesive even in dense urban environments where multiple groups live close together: each group has its own olfactory signature.

Talking Within the Mischief

Rats do not rely on smell alone. They are also surprisingly vocal, though most of their communication happens at frequencies too high for human ears. Adult rats produce structured ultrasonic calls that serve different social functions, from signaling distress to expressing positive affect during play or mating. The transition from the broad, relatively simple isolation calls that pups make to the well-organized adult vocal repertoire reflects how important vocal communication is to their social lives.⁶

Two general frequency bands matter most. Calls around 22 kilohertz are associated with negative situations: a rat that is threatened, in pain, or socially defeated produces low-frequency calls that seem to warn nearby colony members. Calls around 50 kilohertz show up during play, social bonding, and mating, and appear to function more like an invitation to interact. Your pet rat is almost certainly chattering away at frequencies you cannot hear, especially during social time with cage mates.

How Rats Teach Each Other What to Eat

One of the more elegant group behaviors in rats is social learning about food. Norway rats transmit food preferences to one another by smelling each other’s breath.⁷ If a colony member returns from foraging and has been eating something unfamiliar, the rats that sniff its breath become more willing to try that same food. The mechanism behind this involves carbon disulfide, a compound present on rat breath. When researchers paired an unfamiliar food with carbon disulfide, rats showed the same enhanced preference for it as they did after smelling the breath of a rat that had actually eaten it.⁸

This system is a clever solution to a dangerous problem. Rats are omnivores that exploit new food sources constantly, but new foods can be toxic. By letting returning foragers serve as taste testers and reading the chemical evidence on their breath, the colony gets information about what is safe without every member having to take the risk of sampling an unknown item. It is essentially crowd-sourced food safety.

Empathy and Helping Behavior

Rats do not just share information within the group. They also help each other in ways that look a lot like empathy. In a well-known experiment, a free rat was placed in an arena alongside a cage mate trapped in a small restrainer. Over several sessions, the free rat learned to open the restrainer and release its companion, doing so deliberately and with increasing speed. The free rats did not open empty restrainers or ones containing an inanimate object, ruling out simple curiosity. And when the setup included a second restrainer full of chocolate, rats typically opened both, liberating the trapped cage mate and then sharing the chocolate rather than hogging it.⁹

Follow-up work has pushed this finding further. A separate study using a different behavioral model showed that rats learn to help a distressed companion even when no direct social contact is possible as a reward, meaning the helping behavior persists in the absence of social interaction. Rats with prior experience helping learned the task faster, suggesting the behavior builds on itself over time.¹⁰ These findings are some of the strongest evidence that prosocial behavior in mammals is not limited to primates.

Why Pups Need the Group

For young rats, the mischief is not optional. Newborn rat pups are born blind, deaf, and unable to regulate their own body temperature. Huddling together in a litter group solves this problem. Clustered pups reduce their exposed body surface area, which slows heat loss and lowers the metabolic cost of staying warm. Research has shown that huddling cuts oxygen consumption and attenuates heat loss, providing physiological benefits similar to those seen in adult mammals that huddle for warmth.¹¹

Rat pups are also active participants in this process, not just passive heat sponges. Comparative work has found that even at eight days old, rat pups exhibit behavioral responses that promote heat retention, adjusting their position within the huddle in ways that improve the group’s thermal efficiency. Their ability to thermoregulate through huddling is better developed than in some other rodent species of similar age, partly because rat pups produce more body heat of their own to contribute to the group.¹² In short, a rat pup born alone in a cold environment is in serious trouble. A pup born into a litter has a built-in survival system.

Urban Colonies and Why Rat Groups Cluster

In cities, rat colonies do not spread evenly across the landscape. Trap-based surveys in urban neighborhoods have found enormous variation in rat abundance from one city block to the next, with trap success ranging from zero to over ninety percent depending on the block.¹³ The pattern is highly clustered: some blocks are essentially rat-free while neighboring blocks support dense colonies.

This patchiness matters for public health because rats carry diseases, and the way colonies cluster geographically also clusters the pathogens they harbor. Studies of urban rat genetics and pathogen carriage have found that related rats tend to live near each other and that their relatively restricted movement patterns help explain why diseases like leptospirosis show up in geographic hotspots rather than spreading uniformly across a city.¹⁴ From a pest-control standpoint, this means that effective rat management has to be block-by-block and colony-by-colony, not citywide with a uniform approach.

Pet Rats and Why You Should Keep More Than One

All of this social complexity explains why experienced rat owners insist on keeping at least two rats rather than one. A solitary pet rat is a rat deprived of nearly everything its brain is wired for: grooming partners, play companions, sleep piles, and the back-and-forth ultrasonic chatter that fills a social group. Single rats tend to become lethargic or anxious, and in several countries animal-welfare guidelines explicitly recommend against housing rats alone.

When you keep a pair or small group, you can actually observe many of the behaviors studied in laboratories and wild colonies. Pet rats groom each other in patterns that reflect social bonds, with subordinate rats grooming dominant ones more frequently. They pile on top of one another to sleep, mirroring the thermoregulatory huddling seen in pups. And they vocalize constantly during play, producing those 50-kilohertz calls that researchers associate with positive emotional states. The mischief, in other words, is not just a charming collective noun. It describes the default mode of rat social life.

Wild Versus Domestic Temperament

If you have ever wondered whether your pet rat would thrive in the wild, the answer is probably not. Domestication has changed the Norway rat’s social behavior in ways that are not always intuitive. Research comparing wild, hybrid, and domestic Norway rats housed together found that domestic rats were actually dominant over wild ones in both spontaneous and competitive interactions. The proposed explanation is partly about size, since domestic rats tend to be heavier, but also about temperament. Domestic rats lack the social inhibitions that wild rats display, engaging in frequent play-driven interactions that effectively bulldoze more cautious wild individuals. Hybrids fell in between.¹⁵

This “bully effect,” as the researchers described it, flips the common assumption that wild animals are tougher. Wild rats are more fearful and conflict-averse, which makes sense: in a natural setting, an injury from a fight can be fatal, so restraint has survival value. Domestic rats, bred for generations in captivity where injuries are treated and food is guaranteed, have lost some of that caution. The result is a friendlier, bolder animal that happens to be socially dominant when the two types meet. It is a useful reminder that domestication reshapes behavior in subtle, sometimes counterintuitive ways.