Squirrels are opportunistic omnivores, but the bulk of their diet is made up of seeds, nuts, shoots, fruits and leaves. Occasionally, squirrels will predate upon lizards, snakes, worms, birds, eggs or insects. Squirrels are equipped with very long incisors that help them to gnaw into the tough shells of nuts.
Squirrels are very adaptable animals, and many have adapted to living in suburban and urban settings. In such places, squirrels continue to eat their natural food when they can find it, but they also consume a large amount of human-produced food, such as trash or pet food. Squirrels may become a serious nuisance for those who install bird feeders in their yards, as they will bully birds off of the feeders and consume large amounts of seed.
Squirrels are important agents of seed dispersal, making them very important partners for the trees that feed them. For example, squirrels are very fond of hickory nuts. While they eat some of these hickory nuts as soon as they find them, they bury or hide others for later retrieval. The squirrels remember where the vast majority of the nuts were stored and eventually return to eat them. However, squirrels occasionally lose some of the nuts or die before they are able to retrieve them. Left-over or lost nuts eventually develop into trees. Because the squirrels are so mobile, trees are able to spread over great distances, while remaining in the same place.