A group of squirrels is called a scurry or a dray. A dray is specifically used to refer to a nest of squirrels and is often used to describe a mother squirrel and her young. Squirrels are typically solitary creatures making scurries somewhat rare.
Squirrels generally live in trees, usually in holes in the trunks or even abandoned nests. Individual squirrels start looking for nests when they start mating, which happens when they are about 1 year old. When squirrels live in groups, they exhibit a certain level of camaraderie; an altruistic behavior that is displayed when something threatens the scurry. They keep each other alert from lurking predators by producing warning calls.