Are Squirrels in the Rat Family? The Rodent Family Tree Explained

No, squirrels are not in the rat family. Squirrels belong to the family Sciuridae, while rats belong to the family Muridae. Both families sit within the order Rodentia, which means squirrels and rats are distant cousins roughly 70 to 80 million years removed, not close relatives. They share the rodent toolkit — ever-growing incisors, no canines, a gap between front and back teeth — but they diverged into separate lineages long before modern rats existed. Calling a squirrel a rat is like calling a wolf a house cat: same broad order, different family.

The Rodent Family Tree: Where Squirrels and Rats Split

Taxonomy sorts living things into nested boxes: order, then family, then genus, then species. Squirrels and rats share only the topmost of those boxes in common. The order Rodentia contains about 2,300 living species, split into roughly 30 families. Sciuridae (squirrels, chipmunks, marmots, prairie dogs) is one family. Muridae (rats, mice, gerbils) is another.

The split runs deeper than family. Rodentia divides into two major suborders. Sciuromorpha, the squirrel-like rodents, includes Sciuridae plus mountain beavers and dormice. Myomorpha, the mouse-like rodents, includes Muridae. That suborder boundary is the real fork in the road, and genetic dating puts it near the boundary of the Cretaceous and Paleogene periods, around 66 to 75 million years ago.

In plain terms: a squirrel and a rat are about as related as a dog and a seal. Both are carnivorans, but nobody confuses the two.

The table below lays out the actual classification side by side.

What Squirrels and Rats Actually Share

The shared traits are real, and they explain why the confusion persists. Both are rodents, and rodents share a distinctive skull architecture and dental setup.

The incisors are the headline feature. Rodent incisors grow continuously at roughly 0.04 to 0.08 inches per week in small species, and they self-sharpen as the enamel wears unevenly. Neither squirrels nor rats have canine teeth, which leaves a visible gap called the diastema between the incisors and the cheek teeth. That gap lets a rodent retract loose cheek skin while gnawing without swallowing it.

Both groups also lack a gallbladder in most species, a quirk shared across much of Rodentia. Both have a similar basic body plan: compact torso, long tail for balance, hind limbs built for bursts of speed. Both cache or hoard food to survive lean seasons.

These are deep rodent inheritances, not signs of close kinship. A possum and a kangaroo both raise young in a pouch, but nobody calls them the same animal. Shared traits from a common ancestor can persist for tens of millions of years after the lineages separate.

How Squirrels Differ From Rats: A Quantified Comparison

The differences are sharper than the similarities, and most are measurable. Skull shape, tooth count, gestation length, litter size, and lifespan all diverge.

The most reliable field distinction is the jaw muscle arrangement. Squirrels have a sciuromorphous jaw, where the masseter muscle originates on the front of the cheekbone and runs forward. Rats have a myomorphous jaw, with a more complex muscle routing through the eye socket area. That difference changes bite mechanics and is the reason a squirrel can crack a hickory nut that would defeat a rat of similar size.

The table below compares the two on the traits people ask about most.

The tail is the fastest field ID. A squirrel tail is a broad plume with hair along its whole length. A rat tail is a naked, scaly appendage with sparse bristles.

The Ground Squirrel and Flying Squirrel Edge Cases

Not every Sciuridae member looks like the park squirrel. The family includes three body plans, and each one trips people up.

Tree squirrels are the classic bushy-tailed climbers in the genus Sciurus. Ground squirrels, including chipmunks and prairie dogs, live in burrows and have shorter, less plumed tails. Flying squirrels glide on a membrane called the patagium, and they are nocturnal, which makes them the squirrel most often mistaken for a rat in a dark attic.

The flying squirrel comparison is the most instructive. A North American flying squirrel weighs roughly 2 to 5 ounces and has large eyes adapted for night vision. A brown rat in the same attic weighs 8 to 18 ounces. The flying squirrel is smaller, has a flattened gliding membrane, and never has the scaly tail. A homeowner who sees a small nocturnal rodent in the rafters should check tail texture before assuming rat.

There is a second edge case worth flagging. A few squirrel species are shrinking. The Mount Graham red squirrel population has hovered near 100 to 150 individuals in recent years, a case where the animal is a conservation concern rather than a pest.

The Names That Cause the Confusion

Language, not biology, drives most of the mistaken identity. Several unrelated animals carry the word "squirrel" or "rat" in their common names, and a few rodents sit right on the boundary.

The most misleading is the "rock squirrel" and similar names, which are true Sciuridae. The bigger trap is the nutria, a South American rodent often called a "river rat." Nutria belong to the family Echimyidae, not Muridae, so they are neither squirrel nor true rat. Muskrats are cricetid rodents, another separate family. Neither is in the rat family despite the name.

Then there is the "squirrel" name applied to non-rodents. The "flying squirrel" is real Sciuridae, but the "squirrel monkey" is a primate, and the "squirrel fish" is a fish. Common names are descriptive, not taxonomic.

The reverse error also happens. People sometimes call a chipmunk a "little rat," but chipmunks are genus Tamias within Sciuridae. That is a squirrel relative, not a rat cousin. The family boundary is the only reliable line.

A useful rule: if the animal has a bushy tail, sits upright to eat, and is active in daylight, it is almost certainly Sciuridae. Those three traits together rule out Muridae in nearly every North American case.

What This Means for Pest Control and Safety

The practical stakes are real, because the two families behave differently around human structures. A rat in a building is a public health issue. A squirrel in an attic is usually a property damage issue, with a much lower disease ceiling.

Rats are the higher risk. Brown rats can carry leptospirosis and rat-bite fever, and they breed fast enough that a small population becomes an infestation in weeks. Squirrels rarely carry rabies, and documented human rabies cases from squirrels are vanishingly rare. The CDC has long treated small rodents and squirrels as low-risk for rabies exposure, though any bite warrants a medical evaluation.

Red flags that change the response:

• A rodent seen in daylight with a bushy tail is likely a squirrel; check the attic for droppings shaped like small rice grains versus larger capsules.
• Droppings that are capsule-shaped and over 0.5 inch long suggest rats, not squirrels.
• Scratching at night points to rats or flying squirrels; daytime scratching points to tree squirrels.
• Gnaw marks on wiring near a nest are a fire risk regardless of species and warrant an electrician's inspection.
• A rodent that does not flee when approached may be sick, and should not be handled barehanded.

The legal layer matters too. In many US states, relocating a live squirrel requires a permit, while rat control falls under general pest rules. Check local wildlife regulations before trapping anything.

How to Tell Them Apart in the Field

Concrete steps resolve the question in under a minute for most people.

Start with the tail. A plume of hair along the full length means squirrel. A scaly, thin tail means rat. This single check settles the majority of sightings.

Next, check the time of day. Squirrels are diurnal, meaning active in daylight. Rats are nocturnal. An animal crossing a lawn at noon is far more likely to be Sciuridae.

Then look at posture. Squirrels sit upright on haunches to eat and hold food in their forepaws. Rats eat crouched with the head down.

Finally, inspect the teeth if you can do so safely. Both have orange-tinted incisors, so tooth color does not separate them. Instead, count cheek teeth on a skull or photo: four to five per jaw side in squirrels, three in rats.

If the animal is inside a building and you are unsure, do not corner it. Contact a licensed wildlife control operator and describe the tail and the activity time. That description usually settles the ID before anyone arrives.

Limits of the Family-Label Question

One caveat matters. Saying squirrels are not in the rat family depends on the modern definition of "family." Family is a human-made rank, and genetic data keeps reshuffling the rodent tree. Some older texts placed more rodents together under looser groupings, which is part of why the confusion persists in popular writing.

The current consensus is stable on the main point. Sciuridae and Muridae are separate families within Rodentia, and that separation is supported by both morphology and molecular phylogenetics. The exact dating of the split is the least settled number, with published estimates ranging from about 66 to 80 million years ago depending on the method and the fossils included. Treat any single "million years ago" figure as an estimate, not a fixed fact.

The counterintuitive takeaway is that the confusion is understandable. Squirrels and rats really do share the rodent design — the incisors, the diastema, the body plan — and that shared design is over 60 million years old. What separates them is not one dramatic difference but a bundle of small ones: the jaw muscle, the cheek tooth count, the tail, the clock they keep, and the family they were assigned. Those bundled differences are what a taxonomist reads as two families, and what a homeowner reads as two very different animals on the lawn.