Second litters often overwinter in the same den with their parents. Muskrats' sexual maturity is reached at about 9 to 10 months of age. Muskrats are basically herbivorous. They feed mainly on aquatic plants such as the roots and stems of cattails, lilies, sedges, and grasses. They may occasionally eat some animal life such as mussels, shrimp, and small fish.
Vegetation is collected and stored during the summer for winter use.
Throughout the winter muskrats remain below the ice for great periods of time eating this stored food and submerged vegetation. Muskrats bring vegetation to these pushups and eat it there. These pushups also provide the muskrats with a protected place above water and away from their den where they can breathe and rest. Repeated use usually keeps the pushups free of ice. During winters with little snow and very cold temperatures, pushups commonly freeze solid.