Squirrel

Squirrels are small to medium-sized rodents belonging to the family Sciuridae. This diverse family includes tree squirrels, ground squirrels, and flying squirrels. It also encompasses animals like chipmunks and prairie dogs. These rodents are found across the Americas, Eurasia, and Africa. Humans have also introduced them to Australia.

Scientists believe squirrels may have originated in North America. This theory is supported by how different lineages spread across the globe. The word "squirrel" dates back to 1327. It comes from Ancient Greek words referring to a "shade tail." This describes the long, bushy tails seen on many species.

Physically, squirrels possess slender bodies and large eyes for excellent vision. Their fur is often soft and silky, though colors vary widely between species. Most squirrels have hind limbs longer than their forelimbs. They also have four or five toes on each foot.

Their feet feature soft pads and sturdy claws for climbing. Tree squirrels have a unique ability to descend trees headfirst. They achieve this by rotating their ankles 180 degrees. This rotation allows their hind feet to grip the bark from the opposite direction. Their teeth follow a rodent pattern with large incisors that grow throughout their lives. A wide gap called a diastema separates these from their grinding cheek teeth.

The bushy tail is a multi-purpose tool for survival. It acts as a counterbalance when a squirrel jumps through branches. It can even function as a parachute during a jump. The tail helps regulate body temperature by pumping blood through it to cool off. It also provides protection from rain, wind, and cold.

When sitting upright, a folded tail can hide a squirrel's shape from predators. Some people even prize squirrel hair for tying fine fishing flies. Because they rely on vision and touch, many squirrels also have vibrissae, or sensory hairs, on their heads and limbs.

Squirrels occupy almost every habitat except polar regions and extremely dry deserts. Most are herbivores that eat seeds, nuts, fruits, and fungi. However, many species are opportunistic and will eat insects or small vertebrates.

Some tropical species have shifted to eating mostly insects. In times of extreme hunger, they may eat birds, snakes, or even small rodents. One recorded instance in Russia involved black squirrels eating a large stray dog. This flexibility helps them survive in diverse environments like rainforests and deserts.

They use specific strategies to store food and survive periods of scarcity.

Food storage, or caching, varies by climate. In temperate zones, squirrels bury nuts in leaf litter or hollow trees. In humid, subtropical areas, burying food can cause mold or premature germination. To prevent this, some squirrels hang nuts or mushrooms on tree branches.

Two flying squirrel species even carve grooves into nuts to fix them to twigs. This is similar to a mortise-tenon joint used in carpentry. This behavior helps forests expand because forgotten nuts sprout in new locations. This process shows how squirrel behavior directly influences forest ecology.

Squirrel life cycles and social structures differ by type. Ground squirrels are often social and live in colonies. In contrast, tree squirrels tend to be more solitary. Most squirrels are diurnal, meaning they are active during the day. However, flying squirrels are generally nocturnal, or active at night.

Young squirrels, called kits, are born altricial. This means they are born naked, blind, and toothless. Females typically care for the young until they are weaned at six to ten weeks. While wild adults live 5 to 10 years, those in captivity can live 10 to 20 years.

Taxonomy divides living squirrels into five main subfamilies. The Ratufinae includes a few large, cat-sized species in tropical Asia. The Sciurillinae contains only one species, the neotropical pygmy squirrel. The largest group is the Sciurinae, which includes 83 species of tree and flying squirrels.

The oldest known fossil, Hesperopetes, dates to the Eocene epoch about 40 to 35 million years ago. This ancient squirrel was similar to modern flying squirrels. Squirrels also exhibit synurbanization, which is the process of thriving in human environments. They have learned to benefit from urban life, though they can become aggressive if human-provided food sources disappear.