A Squirrel are members of the family Sciuridae, a family that includes small or medium-size rodents. The squirrel family includes tree squirrels, ground squirrels, chipmunks, marmots (including woodchucks), flying squirrels, and prairie dogs amongst other rodents. Squirrels are indigenous to the Americas, Eurasia, and Africa, and were introduced by humans to Australia. The earliest known fossilized squirrels date from the Eocene period and are most closely related to the mountain beaver and to the dormouse among other living rodent families.
The word “squirrel”, first attested in 1327, comes from the Anglo-Norman esquirel which is from the Old French escurel, the reflex of a Latin word sciurus. This Latin word was borrowed from the Ancient Greek word σκίουρος, skiouros, which means shadow-tailed, referring to the bushy appendage possessed by many of its members.The native Old English word for the squirrel, ācweorna, survived only into Middle English (as aquerne) before being replaced. The Old English word is of Common Germanic origin, cognates of which are still used in other Germanic languages, including the German Eichhörnchen (diminutive of Eichhorn, which is not as frequently used), the Norwegian ikorn/ekorn, the Dutch eekhoorn, the Swedish ekorre and the Danish egern.
Squirrels are generally small animals, ranging in size from the African pygmy squirrel at 7–10 cm (2.8–3.9 in) in length and just 10 g (0.35 oz) in weight, to the Laotian giant flying squirrel at 1.08 m (3 ft 7 in) in length and the Alpine marmot, which weighs from 5 to 8 kg (11 to 18 lb). Squirrels typically have slender bodies with bushy tails and large eyes. In general, their fur is soft and silky, though much thicker in some species than others. The coat color of squirrels is highly variable between—and often even within—species.
In most squirrel species, the hind limbs are longer than the fore limbs, while all species have either four or five toes on each paw. The paws, which include an often poorly developed thumb, have soft pads on the undersides and versatile, sturdy claws for grasping and climbing. Tree squirrels, unlike most mammals, can descend a tree head-first. They do so by rotating their ankles 180 degrees, enabling the hind paws to point backward and thus grip the tree bark from the opposite direction. Squirrels live in almost every habitat, from tropical rainforest to semiarid desert, avoiding only the high polar regions and the driest of deserts. They are predominantly herbivorous, subsisting on seeds and nuts, but many will eat insects and even small vertebrates. As their large eyes indicate, squirrels have an excellent sense of vision, which is especially important for the tree-dwelling species. Many also have a good sense of touch, with vibrissae on their limbs as well as their heads.
Many juvenile squirrels die in the first year of life. Adult squirrels can have a lifespan of 5 to 10 years in the wild. Some can survive 10 to 20 years in captivity. Premature death may be caused when a nest falls from the tree, in which case the mother may abandon her young if their body temperature is not correct. Many such baby squirrels have been rescued and fostered by a professional wildlife rehabilitator until they could be safely returned to the wild, although the density of squirrel populations in many places and the constant care required by premature squirrels means that few rehabilitators are willing to spend their time doing this and such animals are routinely euthanized instead.
Because squirrels cannot digest cellulose, they must rely on foods rich in protein, carbohydrates, and fats. In temperate regions, early spring is the hardest time of year for squirrels because the nuts they buried are beginning to sprout (and thus are no longer available to eat), while many of the usual food sources have not yet become available. During these times, squirrels rely heavily on the buds of trees. Squirrels, being primarily herbivores, eat a wide variety of plants, as well as nuts, seeds, conifer cones, fruits, fungi, and green vegetation. Some squirrels, however, also consume meat, especially when faced with hunger. Squirrels have been known to eat small birds, young snakes, and smaller rodents, as well as bird eggs and insects. Indeed, some tropical squirrel species have shifted almost entirely to a diet of insects.
Predatory behavior has been observed in various species of ground squirrels, in particular the thirteen-lined ground squirrel. For example, Bernard Bailey, a scientist in the 1920s, observed a thirteen-lined ground squirrel preying upon a young chicken. Wistrand reported seeing this same species eating a freshly killed snake. Whitaker examined the stomachs of 139 thirteen-lined ground squirrels and found bird flesh in four of the specimens and the remains of a short-tailed shrew in one; Bradley, examining the stomachs of white-tailed antelope squirrels, found at least 10% of his 609 specimens’ stomachs contained some type of vertebrate, mostly lizards and rodents. Morgart observed a white-tailed antelope squirrel capturing and eating a silky pocket mouse.
The living squirrels are divided into five subfamilies, with about 58 genera and some 285 species. The oldest squirrel fossil, Hesperopetes, dates back to the Chadronian (late Eocene, about 40–35 million years ago) and is similar to modern flying squirrels. A variety of fossil squirrels, from the latest Eocene to the Miocene, have not be assigned with certainty to any living lineage. At least some of these probably were variants of the oldest basal “protosquirrels” (in the sense that they lacked the full range of living squirrels’ autapomorphies). The distribution and diversity of such ancient and ancestral forms suggest the squirrels as a group may have originated in North America.
Apart from these sometimes little-known fossil forms, the phylogeny of the living squirrels is fairly straightforward. The three main lineages are the Ratufinae (Oriental giant squirrels), Sciurillinae and all other subfamilies. The Ratufinae contain a mere handful of living species in tropical Asia. The neotropical pygmy squirrel of tropical South America is the sole living member of the Sciurillinae. The third lineage, by far the largest, has a near-cosmopolitan distribution. This further supports the hypothesis that the common ancestor of all squirrels, living and fossil, lived in North America, as these three most ancient lineages seem to have radiated from there; if squirrels had originated in Eurasia, for example, one would expect quite ancient lineages in Africa, but African squirrels seem to be of more recent origin.
The main group of squirrels also can be split into three subgroups, which yield the remaining subfamilies. The Sciurinae contains the flying squirrels (Pteromyini) and the Sciurini, which among others contains the American tree squirrels; the former have often been considered a separate subfamily, but are now seen as a tribe of the Sciurinae. The pine squirrels (Tamiasciurus), on the other hand, are usually included with the main tree squirrel lineage, but appear to be about as distinct as the flying squirrels; hence, they are sometimes considered a distinct tribe, Tamiasciurini.
Two of the three subfamilies are of about equal size, containing between nearly 70 and 80 species each; the third is about twice as large. The Sciurinae contains arboreal (tree-living) squirrels, mainly of the Americas and to a lesser extent Eurasia. The Callosciurinae is most diverse in tropical Asia and contains squirrels that are also arboreal, but have a markedly different habitus and appear more “elegant”, an effect enhanced by their often very colorful fur. The Xerinae—the largest subfamily—are made up from the mainly terrestrial (ground-living) forms and include the large marmots and the popular prairie dogs, among others, as well as the tree squirrels of Africa; they tend to be more gregarious than other squirrels, which do not usually live together in close-knit groups.
Even though it is very unlikely to encounter a rabid squirrel, it is still a good idea to know the signs of rabies infection. The rabies virus affects the central nervous system, usually producing encephalitis or inflammation of the brain. This condition leads to the symptoms usually associated with rabies, including paralysis, blindness or sensitivity to light, loss of balance, aggression, confused behavior and mood changes. The classic symptom of excessive saliva or foaming at the mouth only sometimes occurs as a result of paralysis in the throat or jaw.
Squirrel bites almost never get infected, but you should not avoid getting medical attention for a bite. The bite that you receive from any squirrel could be very deep, and you must receive medical attention even if it will not get infected. Medical professionals prefer to be cautious when you are bitten, but rabies shouldn’t be too much of a concern unless there have been reported rabies outbreaks in your area. It is hard to account for the other animals in the wild that might bite squirrels. Rabies infested animals that bite squirrels in the wild almost never pass rabies on to squirrels. It is possible for squirrels to get rabies from a bite, but it is nearly impossible. A reported outbreak of rabies in your area likely does not apply to the squirrel that recently bit you simply because squirrels almost never get rabies.
One of the most common signs of rabies is weird or unexpected behavior. This uncharacteristic behavior usually takes one of two forms: extreme aggression or unusual docility. Aggressive animals may be vicious, snarling and biting while docile animals seem to lose their instinct to avoid humans and appear unusually calm and approachable. There are other diseases that bear similarities to rabies. In some animals, the symptoms of distemper can look like rabies. Specifically in squirrels, the roundworm brain parasite brings symptoms remarkably like those associated with rabies.
When it comes to wild animals, including squirrels, the best choice is to avoid interacting with them altogether since animals can carry rabies for months before they show symptoms. It is especially important to avoid animals that exhibit strange or unexpected behavior. Anyone who receives a risky animal bite or other exposure to rabies should contact a medical doctor or public health official immediately.
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