The average litter contains five or six young with litter sizes ranging from one to eleven. The young muskrats, blind and naked at birth, are raised either in a nest chamber within the muskrat house or in a den in the bank. They remain in the nest for three or four weeks when they move out to fend for themselves. Muskrats weigh less than an ounce at birth and grow rapidly, reaching adulthood in less than a year. Average adult muskrats weigh from two to two and a half pounds.
Muskrats are somewhat active during the day but most of their activity takes place at night.
They do not hibernate during the winter but live in relative comfort in their well constructed houses or in bank dens. Both their houses and dens have entrances under the water so even when the area is frozen over, they can swim about and gather roots and stalks of aquatic plants for food. Foliage, roots, and bulbs of aquatic plants such as cattail, bulrush, pondweeds, and sedges. Muskrats also eat corn and some other terrestrial plants when readily available and occasionally eat frogs, snails, and clams. Although they are somewhat more expensive than conventional traps, they more than pay for this difference by preventing muskrats from escaping from your trap.