The visual and behavioral similarities between squirrels and rats often lead people to wonder if they are essentially the same animal. Both are highly adaptable mammals frequently seen in human-dominated landscapes, displaying a tendency to gnaw and forage. While they share a deep common ancestry and a fundamental biological classification, the two groups have evolved along distinct paths. This evolution has resulted in significant differences in their anatomy, ecology, and interaction with human environments. Understanding these distinctions is important for proper identification.
Shared Membership in the Rodent Order
Squirrels and rats are both members of the Order Rodentia, which is the largest order of mammals, containing nearly half of all mammal species. The defining characteristic that unites every animal in this order is a specialized dental arrangement for gnawing. Rodents possess a single pair of continuously growing, chisel-like incisors in both the upper and lower jaws.
These prominent front teeth have hard enamel on the front surface and softer dentine on the back, ensuring that the unequal wear keeps the incisor edge razor-sharp. Because these teeth grow throughout the animal’s life, rodents must constantly gnaw on hard materials to keep them worn down and prevent overgrowth. A gap, known as the diastema, separates the incisors from the cheek teeth, which are used for chewing plant matter.
Key Biological Distinctions
Despite their shared membership in the Rodentia order, squirrels and rats belong to different taxonomic families, reflecting millions of years of evolutionary divergence. Squirrels belong to the family Sciuridae, while common rats (like the Norway and roof rat) are part of the family Muridae. These differences are clearly visible in their physical traits, especially the tail. Squirrels have a thick, bushy tail covered in fur, which they use for balance, communication, and warmth. In contrast, rats possess a thin, often scaly and hairless tail that serves primarily as a thermoregulatory organ to dissipate body heat.
Another major distinction is their daily activity cycle. Most species of squirrels are diurnal, meaning they are active during the day, relying on their keen eyesight to forage and navigate. Rats, however, are predominantly nocturnal, with their activity peaking during the night and twilight hours.
Their primary habitats and nesting habits also vary significantly. Many squirrels, known as tree squirrels, are arboreal, building large nests of leaves and twigs high up in tree cavities or on branches. Common rats are terrestrial, often preferring to burrow underground or establish nests in dark, secluded areas like wall voids, basements, and sewers. Squirrels have large hind legs and small forepaws that function like hands for climbing and manipulating food, whereas rats have a more generalized body shape suited for scurrying and burrowing.
Impact on Human Environments
The distinct behaviors and habitats of squirrels and rats lead to different types of interactions and damage in human environments. Rats are frequently associated with structural damage and contamination, often invading homes to find food, shelter, and nesting sites. They are notorious for chewing through various materials, including walls, pipes, and electrical wiring, which can cause significant damage and fire hazards.
Squirrels, while also capable of causing damage, tend to focus their destructive behaviors on areas such as attics, where they might chew on insulation and wiring to create a nest. They are also well-known for disrupting gardens and bird feeders while foraging for nuts and seeds.
The perception of risk is also different. Rats, particularly non-native species, are historically linked to a higher risk of disease transmission to humans, including hantavirus and rat-bite fever. While squirrels can also carry diseases and parasites, the risk of direct disease transmission to humans is lower than with rats.