The speed of crabs varies depending on the species and their size. Generally, crabs are not known for being fast runners, but they can move quickly when they need to. Some crabs, like blue crabs and Dungeness crabs, can scuttle sideways at a pace of around 4-5 miles per hour, which is relatively fast for their size. Other species of crabs, such as hermit crabs and fiddler crabs, move much more slowly. Overall, crabs have adapted to move in a variety of terrains, including in water, on sand and rocks, and even in mangrove swamps.