The common perception of a squirrel as a strict vegetarian, constantly foraging for nuts, is biologically inaccurate. Squirrels are classified as opportunistic omnivores, meaning they consume both plant and animal material to survive. While the vast majority of their diet consists of seeds, nuts, and other vegetation, their ability to adapt and consume protein from other sources defines their classification. This flexibility is a significant factor in how the more than 200 species of squirrels, which include tree, ground, and flying squirrels, have managed to thrive across diverse global habitats.
The Primary Diet of Plant Matter
Squirrels are predominantly herbivorous, relying on a wide variety of plant foods that provide the necessary energy and nutrients for their active lifestyle. Their diet is heavily focused on seeds and nuts, which are high in fat and carbohydrates and serve as dense, storable sources of energy. These hard-shelled items, such as acorns, hickory nuts, and walnuts, are important food items, especially in preparation for leaner seasons.
Beyond these familiar staples, squirrels consume a large amount of other vegetation throughout the year. They readily eat fruits and berries when available, along with tree buds, flowers, and the inner bark of certain trees. Fungi, including various species of mushrooms, are also a significant part of their diet, providing nitrogen and minerals. They are also known to consume green vegetation and conifer cones.
Evidence of Omnivorous Consumption
Squirrels’ consistent consumption of non-plant food sources confirms they are not vegetarians. When the opportunity arises, squirrels actively seek out protein and fat from animal matter. Insects are a common addition to their diet, including beetles, grubs, and caterpillars, which provide a concentrated source of protein.
Squirrels will also prey on vulnerable vertebrates, often consuming bird eggs and nestlings to supplement their energy needs. They have been documented eating small rodents, such as voles, and even small snakes. This carnivorous behavior is often driven by biological demands, such as the need for extra protein and calcium for nursing mothers or to meet energy requirements when plant foods are scarce.
Squirrels are also known to consume carrion and will gnaw on bones. Gnawing on bones provides trace minerals and is a method for rodents to wear down their continuously growing incisors. The most carnivorous members of the family, such as the nocturnal Southern flying squirrel, rely heavily on a diet rich in animal matter, including insects and small vertebrates.
Adapting the Diet for Seasonal Survival
A squirrel’s diet is highly dynamic and is primarily dictated by the availability of food throughout the changing seasons. The autumn months are dedicated to consuming and burying high-calorie, storable foods like hard mast (nuts and acorns) to create a winter reserve. This behavior, known as scatter hoarding, is a survival mechanism that ensures access to energy when fresh forage is unavailable.
During the winter and early spring, when buried caches may be depleted or inaccessible, the diet shifts to less nutritious items. Squirrels rely on tree buds, bark, and any remaining seeds to survive the cold months. Consumption of animal matter, such as insects or bird eggs, becomes more important, providing a necessary protein boost to compensate for the scarcity of high-energy foods.