About Squirrels


Welcome! Here is in very brief some information about one of the most important and most amazing species : Squirrels.


The following information refers mostly to North American species of Squirrels, due to the lack of more study about the species that live in other continents. We need our members' input and help to develop the knowledge about other species. This is an important part of our work .

Thank you.



The species described below are North-American species, native and introduced. They represent only a fraction of the number of squirrels' species that inhabit the Earth .

Eastern Gray Squirrel (Sciurus carolinensis)-6 subspecies. Color: mixed dark and light hair, colors from gray, tan or light brown to dark brown and black. Body length : 385-530 mm; tail: 150-250 mm. Weight:330-750 gm. 22 teeth.

Western Gray Squirrel (Sciurus griseus)-3 subspecies. Color: Gray with white hair, belly lighter, some red.\, yellow or brown coloration on upper body or backs of years, body has distinct separation between coloring on back and on belly, tail is large and bushy, with nuances of gray, white and black. Body length: 510-579 mm, tail :74-80 mm. Weight: 340-964 gm. 22 teeth.

Fox squirrel (Sciurus niger)-10 subspecies. Color: Black color phase differentiated from Abert's squirrel by distinct ear tufts on Abert's; reddish-brown with lighter belly, three color phases: gray over yelow,reddish-brown, black; white or light-colored individuals common. Body length: largest tree squirrel, 454-698 mm, tail :200-330 mm. Weight: 504-1062 gm.20 teeth.

Red squirrel (Tamiasciurus hudsonicus) -25 subspecies. Color: reddish brown or rust, tan gray yellowish or reddish with pale to white belly. Body length : 272 -385 mm, tail: 92-158 mm. Weight: 145-260gm. 22 teeth.

Douglas squirrel (Tamiasciurus douglasii) -4 subspecies. Color: Body rust, olive brown, or reddish brown to gray; belly yellow to orange. Body length: 270-345 mm, tail: 102-156 mm. Weight: 150-300 gm.22 teeth.

Southern flying squirrel ( Glaucomys volans) -4 subspecies. Color : gray, olive, light brown, or brown- white with a white to cream colored belly; black ring around the eye.Presence of the patagium, a flap of skin used to glide.Body length : smallest tree squirrel,125-175 mm, tail:75-120 mm. Weight :40-98 gm. 22 teeth.

Northern flying squirrel (Glaucomys sabrinus) -24 subspecies. Color : brown with lighter to white belly. Presence of patagium, a flap of skin used for gliding. Body length: 263-368 mm, tail: 115-180 mm. Weight: 45-140 gm. 22 teeth.

Abert's squirrel (Sciurus aberti) -9 subspecies. Large size, with very distinctive ears, large with vertical tufts of hair.Color : dark-brown or black, three color phases:dark gray body with white belly, gray tail fringed with white, all black including tail, brown including tail. Body length: 463-584 mm, tail: 195-255 mm. Weight: 681-908 gm. 22 teeth.

Thirteen-lined Ground squirrel (Spermophilus tridecenlineatus). Color : tan ground squirrel with 13 brown-and-white stripes broken up into spots along its back and sides. Body length 5-6" long, tail: 2-5" long. Weight: 4-10oz. Signs : a hole or burrow entrance with many little pathways leading away from it.

Golden-mantled Ground squirrel ( Spermophilus lateralis). Color : ground squirrel with reddish head and shoulders and a white stripe with black stripes on each side. Body length : 6-8".

White -tailed Antelope squirrel ( Ammospermophilus leucurus) . Color: ground squirrel with white side stripes, brownish yellow body in summer and gray in winter, tail white underneath. Body length :5-6".

Black-tailed Prairie Dog ( Cynomys ludovicianus). Color : the only species with a black tip on the tail; large ground squirrel with a light brown back. white belly, and thin, black-tipped tail. Build vast prairie-dog towns. Body length: 10-11", tail : 3-5". Weight: 2.5-4 lb.

White -tailed Prairie Dog (Cynomys leucurus). Color :prairie dog with a short white-tipped tail, yellow nose and small ears. Body length: 12 ".

Utah Prairie Dog (Cynomys parvidens). Color : very similar with the White-tailed but slightly redder. Body length: 11-12".


First ancestors of modern squirrels were roaming the Earth in Eocene (about 50 million years ago) and are known as Paramyinds, them being the earliest form of rodents. Some of them were similar with today's squirrel, excepting in much larger size (60 cm) .

The Family Sciuridae is one of the 31 Families belonging to Rodentia Order. By far the largest Order of Mammals, comprising 1625 species, Rodentia Order makes almost half of the total number of Mammals Species.The Squirrel Suborder of Rodents includes: Scaly-tailed Squirrels, Tree Squirrels,Beavers, Springhares, Pocket Gophers, Kangaroo Rats and Mountain Beavers.

Definition of Mammals:Animals with spinal columns (vertebrates)that have hair and and the females have mammary glands that produce milk.

Definition of Rodents: Mammals that have unique incisors that are used for gnawing.

The Family Sciuridae includes about 250 species of squirrels. Due to the large variety of colors within one species, to determine accurate where one particular individual belongs presents a serious challenge even for experienced naturalists.

Squirrels live around the world, with very few exceptions: Australia, Madagascar and Antarctica. They vary slightly in color, size and some characteristics. The smallest squirrel lives in Africa, the pygmy squirrel (Myosciurus pumilio) with only 5 inches in length. while the largest (Eupetaurus cinereus) known as Wolly flying squirrel is two feet long with another two feet long tail and lives in Pakistan, high in the mountains. This squirrel was believed until recently to be extincted; it is said that its crystallized urine is used as aphrodisiac. Another large squirrel is the Indian giant squirrel (Ratufa Indica) that lives in tree,s in India, Borneo, Java and Sumatra. Among the species most known in the world are: in Africa , the African giant squirrel (Protoxerus stangeri), the African bush squirrel (Paroxerus)and the sun squirrel (Heliosciurus); in Europe there are flying squirrels( Polatouche) and European red squirrel (Sciurus vulgaris), red and white Flying squirrels in Asia and several species in North America : Eastern gray squirrel (Sciurus carolinensis), Western gray squirrel (Sciurus griseus), Northern flying squirrel (Glaucomys sabrinus) ,Southern flying squirrel (Glaucomys volans), Arizona gray squirrel (Sciurus arizonensis), American red squirrel (Tamiasciurus hudsonicus), Douglas Squirrel (Tamiasciurus douglasii) and Albert's squirrel (Sciurus aberti).


The squirrels live in a wide geographic area around the world, so their diet varies according to the food available. Most common are the tree squirrels and their natural diet consists in products generated by the trees, such as: nuts (acorns, hickories, pecans, walnuts,hazelnuts, chestnuts, beechnuts ) produced by hardwood (deciduous )trees and pine cones produced by softwood (conifers ) trees. Another major part of a tree squirrel's diet , also produced by trees is the tree-seeds and tree fruits and berries, food supplied by the following species :apple, arbor vitae,ash, basswood, birch, bittersweet, black locust, blackberry, blackgum, blueberry, buckeye, butternut, cherry, cranberry, currants, dogwood, douglas fir, elderberry, elm, fir, flowering dogwood, grape, howthorn, hemlock, hornbeam, huckleberry, incense cedar, kinnikinnick, maple, mockernut, mountain ash, mulberry, osage-orange, pear, raspberry, salal, sedge, serviceberry, spruce, sweetgum, sycamore, tulip tree.

In addition with food produced by trees, squirrels' diet includes a variety of fungi -Agaricus Magnificus, Amanita Frostiana, Coprinus Comatus , Panus Strigosus- , buds, insects, tweeds, seeds, flowers, pollen. In regions with domesticated crops and garden plants, squirrels eat field corn, sweet corn, wheat, soybeans, blueberries, oats and buckwheat. Due to the encroachment of humans habitate in wilderness, which resulted in replacing their natural forest food with crops, the latest become part of surviving food for squirrels, placing them in a perilious, antagonistic position with humans.

Occasionally, squirrels gnaw on animal bones, antlers or turtle shells.There are several theories about their reasons, which could be to control their growing teeth, as a source of minerals or as a supplement of nutrients for mother-squirrels after giving birth.

One of the most amazing relationship observed in nature is between squirrels and the trees. The tree is the "house" and the source of food for squirrels, so they love their trees. The relationship between squirrels and trees is ages old. For milions of years, squirrels contributed at maintaining the forests by burying the seeds and nuts at optimum level in the ground (about 2 cm) so the new tree can grow. By consuming the excess of nuts , seeds , fruits and berries, the squirrels help the tree to balance its production, prevents the branches to break and help at directing the flow of nutrients to less seeds, so those grow stronger and healthier. At the white oak tree, it is known that squirrels dig a small hole in the acorn before burying it, to prevent the nut to germinate during winter. While this process benefits the squirrel by helping her to use the full nutritional value of the acorn, also benefits the tree and the forest by preventing an excess of new trees on a small area. The squirrel eats the insects that threatens the trees and destroys brunches affected by diseases by cutting them down.

A specific example of the complex, beneficial relationship that exists between squirrels and their trees is this between Fox squirrel and longleaf pine. At the root system of the pine grows a fungi that depends on the tree for carbohydrates. As it grows, the tree extracts from it hormones, regulate its nitrogen and extends the area to absorb water and nutrients from the soil. The squirrel consumes the fungi, while releasing the spores of the fungi ( which are indigestible) on another tree.

Along to their natural diet and local diet, the squirrels enjoy a seasonal diet, such as : unopened pine corns,maple samaras, annual and perrenial flowers, corms, bulbs, insects and fungi in Spring, berries, fruits, acorns, fungi in Fall, cached pine cones , nuts and dried fungi in Winter.


Hoarding is a characteristic of very few species of animals, mostly rodents, to store the food in order to survive periods with scarce resources or to protect it from other animals. Unique for squirrels and of a major importance is that, among all the species that use hoarding, the tree squirrel is the only one that bury the nuts at the optimum depth (1-5.5 cm) so the nut can germinate.

The squirrels use hoarding both from necessity as well as instinct. They store the food in order to preserve it for periods of luck of resources , such as Winter months, sometimes for periods in which the production of nuts is lean, as it happens with coniferous and acorn trees, which have fluctuating levels of producing nuts. While very seldom found in the animal world, the hoarding behavior is an unique, powerfull characteristic of a species that contribute greatly at its survival; while most of species are in tremendous difficulties when faced with Winter or other factors that affect the food supply, the once that use hoarding have a clear advantage.

The squirrels use both types of hoarding : scatter ( dispersed ) and larder (stored together). The method used varies according with the species (red squirrels use more larder) and according with the kind of food stored. The squirrel can bury a nut as far as 15 meters away from the tree that produced it, but mostly the nuts are buryed close to the source. It is estimated that only about half of the nuts buryed are ever retrieved. In retrieving them squirrels use their sense of smell and , some times, visual signs.

It is of an amazing complexity the way the squirrels treat various food before storing it, as they prepare it in order to preserve the nutritious value of each food. The mushrooms are first being dried (by impaling them in a brunch) and then stored in dry places, such as tree cracks. To retain the moisture in the cones, they are being purchased when still green and stored under piles of debris made from squirrels' meals left-overs and accumulated in the same place.This middens are mostly used by red squirrels and the hoarding is larder. They can contain up to 15 bushels of cones. The acorns are being prepared before storing by making a notch in it, while the chestnuts are being carefully piled from the outher skin. The hoarding is part of squirrels'nature and it is done without teaching by some very young squirrels. It is done less careful in areas with year-around abundance of food supply. Aside from nuts, the squirrels store other food , such as fruits and berries. The stored nuts are often found and stolen by other squirrels. Squirrels do still caches of food from birds (such as blue jays) and other animals. They tend to defend the larder hoards , while ignoring the scattered buryed nuts.


The squirrels' nest varies slightly according with the species. Generally, the nest is build high on a brunch tree, and resembles a large bird's nest, excepting the fact that do not have an open area. It is constructed from small brunches and twigs filled with leafs in a spherical shape. The squirrels that habitate in coniferous area replace the leafs with smaller twigs. Inside, the nest has a filling of soft and insulating materials, such as shredded bark, moss,small leaves and anything else that do the job. While the nest appears large, the cavity inside it used by squirrels is very small, with a diameter of about 8 inches. In Winter months, the squirrels prefer the natural nest offered by tree cavities. While these cavities are formed by rot, insects or woodpeckers, the squirrels can enlarge them with their teeth. Like the brunch nest, the tree cavities nest is lined with soft materials. A squirrel's nest can have two or more doors, for security reasons.

The construction of the nest is fast, sometimes being almost finished in one day; more material is added in time. Some squirrels have more than one nest, this serving the purpose to elude predators and to sanitize against parasites. The squirrels' nest is clean of body wastes, except flying squirrels, which use a corner of their nest as latrine. Also the actual building of the nest is a simple process, the squirrels have a number of criteria in choosing the location , such as : exposure to predators, food supply, the density of the population, the overall quality of the environment, the sex, and stage of the squirrel. For example, a soon-to-be mother builds a nest in a tree that provides food for the season when her off-springs will be ready to go out, or in the vicinity of such tree. An adult male do not have this criteria when building his nest. As thinner the tree brunch it is, as more safety will offer to squirrel against predators such as raccoons, which , due to their large size, cannot access squirrel's nest.

The squirrels are known as being territorial animals. The degree in which this is happening varies again according to the species. The red squirrel is one of the most aggressive in defending her territory, while other species do not exhibit this behavior, excepting when it is a mother squirrel. Another factor is the food supply and the dynamics among one particular population . The gray squirrel, for example, can have social behavior; in Winter months, a number of gray squirrels occupy together the same tree cavity, or a number of mother rise together their babies in one nests, if it proves to be safe and well sheltered. Shared nests are particularly used by flying squirrels.


Squirrels' mating behavior and period of year varies slightly from species to species. Most of squirrels have one or two mating seasons, during January and February in Winter and June, July in Summer. There are a number of other factors that contribute at a squirrel 's capability to mate and reproduce in both seasons, and there are several theories in this issue, same relating it with the food availability. Mating in itself consist in a series of wild chases that can be observed during these months ; when looking high at the tree canopy, it is noticeable an unusual behavior : most of the squirrels in a given area are busily engaged in chasing each other while emitting a variety of sounds. The ones running away from the chase are the young squirrels. A number of males are actively pursuing one female, while trying to establish dominance among themselves. During mating, the squirrels, mostly the males, are so absorbed in the process that they are in total disregard of any external threat, becoming an easy pray . The female at this time is in "estrus". While it is believed that the smell attracts the males and that the one that succeeds in mating is the oldest male, it is little known what is the criteria of a female squirrel in choosing her mate. The mating lasts maximum 2 minutes , after which the male role ends. The new-born are being exclusively raised by the mother. Remarkably, the squirrels reproductive apparatus have some anatomical differences from species to species, and at least one unique biological process happens during copulation: after ejaculating, the male releases a wax-like substance that blocks the eggs from being fertilized by other males. There are other interesting processes in this subject that remain to be studied.

The period of gestation, again ,varies with the species and with the size: the smaller the squirrel, the shortest the gestation length (red squirrel and flying squirrels have a gestation period less than 40 days, while for gray squirrels, fox squirrels and abert squirrels the gestation period is between 38 and 46 days).

The squirrels gives birth to litters containing 2-5 babies, some times more, according to species and environmental factors. The new-born are weight very little (less than 18 grams), are blind, furless and deaf. Fur starts to grow after two weeks and the eyes and ears open after 4 weeks. After two months they stop eating milk, replacing eat gradually with solid food and after three months they are ready to go out from the nest, after a number of teaching lessons from the mother. They are ready to build their own nest after 6 months, also they can make attempts (and sometimes succeed) much earlier. In the first two years of life, the babies squirrels are very vulnerable to the threats of predators and environment. A squirrel that have 50 per cent of her litter reaching adulthood is considered successful.

The mother-squirrel is sophisticated, loving , caring and protective. She chooses the nest carefully for her babies before giving birth and spent her time entirely, except when out to forage for her own food, with her litter. It is very interesting to observe her motherly expression of love , and at the future time we will dedicate a large portion to this study. When the nest it is not safe any longer, the mother moves the young to another location, by carrying them in her mouth one by one. She holds them gentle from the belly, while the body of the baby is wrapped around her mouth.


Like most living species, squirrels are subjected to diseases and parasites.

Together with the common organisms that affects a large number of mammals, like ticks, mites, fleas, lice, tapeworms, threadworms and protozoa, the squirrels are affected by parasites that can seriously harm or kill them. Two of most common such parasites are the "mange mite" and the "warble fly". The first lays its eggs inside squirrel's skin, while the larvae burrow into hair's follicles. The squirrel looses fur on a large area of its body ; however, the look of a squirrel affected by mange can be misleading, as the same appearace can be the result of severe lack of nutrients (lack of food) . Warble fly of the genus Cuterebra is specialized in attacking squirrels. It lays its eggs in squirrels' nests and the larvaes borrows in the skin; the skin swallows into cysts. Both of these parasites can be deadly, if the squirrel's body is weak due to poor nutrition.

Several viruses are most known to affect squirrels: forms of encephalitis viruses, plague, leptospirosis,tularemia, tetanus, leporipoxviruses, Silverwater virus, Powassan virus, ringworm and mange. Rabies are very rare among squirrels.

While the squirrels make for a tiny part of any predator's diet -just around 10%- they have an assorted number of natural enemies, on the air, land and water.

The most dangerous predator for squirrels is a small carnivor, the pine marten (Martes americana), due to its agility and speed in climbing the trees. The raccoon is another, and it is believed that , due to the fact that the raccoons share with the squirrels almost all habitats, it is one of the major sources of death. Most vulnerable to all the predators are the young squirrels, in their first two years of life. Common predatory birds are: red-shouldered hawk, goshawk, great horned owl. On the ground known to attack squirrels for food are: tree-climbing snakes, martens, weasels, ground snakes, opposums, foxes, coyotes and bobcats. During the migration periods ( also rare, squirrels migrate ), when forced to swim, squirrels are being eaten by some species of large fish :pike, gar, trout, bass and other.

In the areas shared with humans, the squirrels experience an even larger rate of mortality, not by their natural predators ( which do not populate humane settlements) but by domestic pets, such as dogs and cats.

Together with a number of other natural and humane factors, the rate of mortality among squirrels is very high, with an estimated 15-25 per cent of young animals surviving their fist year.It is appreciated that , while the life-span to a squirrel can be 11 years, the animals living in wilderness rarely reach more than 7 years, while the city squirrels die within first 5 years.



There are many interesting, mysterious facts about squirrels , such as the phenomenum of migration. We hope , in time, we will contribute at solving some of these puzzles.

The squirrels are not migratory animals. However, once in a while they migrate in large masses of hundreds and thousands, during one day and one night. What really triggers this unusual phenomenum ? One theory is that the lack of food and their emerging need to seek grounds with more resources in order to survive. Even more interesting, what is the level of communication that prompts such a large number of animals to make a quiq decision to leave at the same time heading for new, unknown territory, far away from where they are born and belong?

During migration, the squirrels have to cross large rivers and, also good swimmers, many of them drawn. Many others ( thousands ) were being mercilessly killed by the humans once they reached the other side of the river. It is recorded that during the 1749 migration in Pensylvania 640 000 squirrels were killed by humans (mostly beaten to death).

In North America there were a handfull of migration of squirrels occurring at different periods of time -1979, 1808, 1842, 1930 , 1968 -in different locations -Pennsylvania, Ohio, Wisconsin, Connecticut. They happened during late summer, early fall. Here is an early record of a migration written by John James Audubon and his collaborator, John Bachman: "Farmers in the western wilds regard them with sensations that may be compared to the anxious apprehensions of the Eastern nations at the flight of the devouring locusts. At such periods, which usually occur in autumn, the squirrels congregate in different districts of the far Northwest; and in irregular troops, bend their way instinctively in an eastern direction. Mountains, cleared fields and narrow bays of some of our lakes , or our broad rivers present no unconquerable impediment. Onward they come, devouring on the way everything that is suited to their taste, laying waste of corn and wheat fields of the farmer; and as their numbers are thinned by the gun, the dog and the club, others fall in and fill up the ranks, till they occasion infinite mischief, and call forth more than empty threats of vengeance."

While the gray squirrel it is believed to engage in migration, there are some reports about Fox squirrel in Pike County, Pennsylvania, described in the following anonymous story: " An immense army of squirrels arrived at the banks of the Delaware River late one night, and commenced its passage by swimming the next morning. The whole population turned out, and boys and men, equipped with large grain sacks and clubs, killed them by the thousands. They kept coming in a continuous stream throughout the morning, and passed on to the woods beyond. Nothing could deflect them from their course, as they were evidently bound for a fixed point."

As Mr. Richard Mallery notes: " Many of these migrations were probably caused by food shortages as well as habitat overcrowding. We solved that for them. We not only reduced their habitat, we reduced the whole species by about 90%. The least we can do now is share a little birdseed with them."