The muskrat, scientifically known as Ondatra zibethicus, is a medium-sized, semi-aquatic rodent found across North America. This mammal gets its common name from the musky odor produced by scent glands, which it uses for communication and territorial marking. The muskrat is the sole extant species within its genus and is the largest member of the subfamily Arvicolinae, which includes voles and lemmings. The species is highly adapted to life in the water, occupying a unique niche in freshwater ecosystems. It has established itself across a vast geographical range, extending from the Arctic Circle down to the Gulf of Mexico, and has also been introduced to parts of Eurasia and South America.
Physical Traits and Identifying Features
An adult muskrat typically measures between 16 and 28 inches long, with approximately half of that length being the tail. The body alone is 8 to 14 inches long, and the animal weighs about 1 to 4 pounds. This size makes it significantly larger than a common brown rat, yet much smaller than the North American beaver, with which it often shares habitat.
The muskrat’s coat is composed of two layers: dense, soft underfur for insulation and longer, dark brown guard hairs that are glossy and water-repellent. This thick, air-trapping fur provides buoyancy and protection against cold water, which is particularly important since they remain active year-round. The fur color ranges from chestnut brown to nearly black, often fading to a lighter gray-brown on the belly.
The most distinctive characteristic is the tail, which is unique among North American rodents. The tail is long, scaly, and laterally flattened, functioning like a rudder to provide directional stability and aid in maneuvering while swimming. Propulsion is primarily achieved using the hind feet, which are large, broad, and partially webbed.
The Muskrat’s Wetland Home
Muskrats prefer still or slow-moving water environments that offer abundant aquatic vegetation. They inhabit a wide variety of wetlands, including marshes, ponds, lakes, streams, and irrigation ditches. Ideal habitats generally have water depths between 15 and 40 inches and contain plants like cattails and bulrushes, which serve as both food and building material.
The species constructs two primary types of shelters depending on the local environment. Along riverbanks and shorelines, muskrats excavate bank burrows dug into the muddy earth. These burrows have an entrance submerged underwater, typically 6 to 12 inches below the surface, leading to a dry living chamber located above the high-water line.
In shallow marshes where bank digging is not feasible, muskrats construct dome-shaped lodges. These structures are built from large piles of vegetation, such as cattail stalks and mud, and can be up to three to six feet wide at the base. Like the burrows, the lodges feature inner chambers and are accessed via underwater tunnels that protect the occupants from predators and weather.
Behavior and Feeding Habits
Muskrats are primarily crepuscular, meaning they are most active during the twilight hours of dawn and dusk, although they can be observed foraging throughout the day. They are exceptional swimmers, capable of remaining submerged for extended periods, usually between 12 and 17 minutes, by reducing their heart rate. This diving ability is enhanced by specialized lips, which close behind their front teeth, allowing them to chew plants underwater without inhaling water.
They generally live in small family groups consisting of a male, a female, and their young, often establishing and defending a defined territory. Muskrats are mainly herbivorous, with aquatic plants forming the bulk of their diet. They consume the roots, stems, and leaves of vegetation like cattails, water lilies, and pondweeds, often eating about one-third of their body weight daily.
While plants are the mainstay, muskrats are opportunistic omnivores and supplement their diet with animal matter. They consume small invertebrates, including freshwater mussels, crayfish, snails, and occasional slow-moving fish or amphibians. During winter, muskrats do not hibernate and must actively forage, sometimes using specialized feeding platforms, or “push-ups,” built under the ice to consume gathered plants and mussels.
Interaction with Humans and the Ecosystem
Muskrats fulfill a significant ecological role as a primary consumer of aquatic vegetation and a source of prey for numerous predators. By foraging and building their lodges, they help create a patchy pattern of open water within dense marshes, which benefits nesting waterfowl and other aquatic species. Their populations naturally fluctuate in cycles, and when numbers are high, their intense grazing can lead to “eat-outs,” where large areas of wetland vegetation are completely removed.
Historically, the muskrat was of considerable economic importance due to its dense, valuable fur, and it was a staple of the North American fur trade. The practice of translocating muskrats for fur farming resulted in their introduction and establishment as an invasive species across parts of Europe and Asia. Today, the species is classified as Least Concern due to its widespread and stable population, despite localized declines in its native range.
The primary conflict with humans arises from the muskrat’s burrowing behavior, which can cause significant structural damage to man-made water controls. Their tunnels undermine the structural integrity of earthen dams, dikes, irrigation ditches, and levees, posing a risk to infrastructure and agricultural fields. In agricultural regions, muskrats can also cause losses by consuming crops, such as rice, that grow near their aquatic habitats.