We have many animals living in habitats all around us that are semiaquatic, which means they spend time both on land and in water. It can be fun to see a critter splish splashing around in the water, but it can also be hard to tell what kind of animal you are seeing.
Beavers, muskrats, river otters and mink are all semiaquatic, and all are brown, making identifying them correctly even more challenging. Otters and mink can be easier to tell apart from the others because both have long bodies. However, beavers and muskrats can be more difficult to tell from one another in the water. Identifying them is much easier on land, where their features are more easily seen.
Beavers and muskrats are both rodents, the largest order of mammals in terms of the number of species. However, they belong to different families. Although they are not closely related, beavers and muskrats have evolved to have many shared behaviors and traits. This is a scientific concept known as convergent evolution.
Another example of convergent evolution is sharks and dolphins. Sharks are fish and dolphins are mammals, but they both have flippers, pectoral and dorsal fins and long, streamlined bodies that help them swim.
When it comes to beavers and muskrats, one main difference between them is their size. Beavers are the largest rodent in North America, and they are considerably bigger than muskrats. A beaver can weigh as much as 100 pounds, but they typically are between 35 pounds and 68 pounds. They are between 39 inches and 47 inches long. Muskrats are much more lightweight than beavers. They weigh only between 2 pounds and 5 pounds. They are also not as long as a beaver, measuring between 16 inches and 25 inches in length.
Both animals have long tails. Beavers' tails measure 10 inches to 13 inches long, and muskrats’ tails are between 7 inches and 12 inches long. However, beaver tails are much wider, usually 3.5 inches to 8 inches wide. Muskrat tails are very thin and rat-like.
Size isn't the only difference in their tails. A muskrat's long, skinny tail is covered in short black hairs. A beaver's large, flat tail is covered in scales and has no hair on it.
Size and tail shape are two key differences between muskrats and beavers, but neither may be obvious when they are in the water. If you see an animal swimming, you may be able to tell whether it's a muskrat or a beaver by how it carries itself in the water. Muskrats usually swim with their heads, backs and tails visible at the water's surface, but beavers normally keep only their heads above water. Beavers use their tails as a rudder to help guide them while swimming, so you won't be able to see it at the water's surface.
Another similarity between these two animals is that both live in lodges. If you happen upon one you may be able to tell which creature lives inside because of some telltale signs. First, a beaver's lodge will be much larger than a muskrat's. The material they use to build is different too. Beavers usually build lodges from wooden material like sticks and logs, and muskrats use other kinds of vegetation, like cattails.
While both animals build lodges to live in, only beavers make dams. Their dams, built from logs and mud, can create new aquatic habitats for both them and a variety of other animals.
In some parts of the United States, telling the difference between these animals is made even more difficult because of the presence of a third animal, the nutria. These animals look similar to beavers and muskrats and also share many of their traits and behaviors.
Nutria are native to South America and were brought to the United States with the intent of creating a fur farming industry. Some of the nutria escaped and others were released, and now these animals live in many coastal parts of the United States, including the Pacific Northwest and Gulf Coast.
Nutria are also brown rodents, and they are also semiaquatic. They are between the size of a muskrat and a beaver, weighing between 10 pounds and 20 pounds. They are about 30 inches long, with a 10-inch rat-like tail covered with a few hairs.
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