Leeches are a vast group of segmented worms. These organisms compose the subclass Hirudinea in phylum Annelida; they're also called annelid worms. Leeches are known for their bloodsucking tendencies. Leeches employ a wide array of animals as hosts, including mammals -- including human beings -- and reptiles and fish. Although they can't walk or run, they are perfectly able to move around, namely by using their swimming and crawling skills.
Leeches spend most of their time within still or sluggish freshwater pools. However, they also are relatively common sights in saltwater and on terra firma within damp dirt. Their approaches to motion generally differ depending on which of these habitats they're in.
Moving in the Water
The majority of leeches can hold their own swimming. When they swim, they make seamless, wavelike movements. The overall impression of their swimming is an elegant one -- far from awkward. The swimming style of leeches is reminiscent to that of eels. They initiate the process by using their anterior suckers to pressure them away from surfaces such as stones, as an example.
Moving on Land
On land, leeches move by controlling their muscles -- both by widening and narrowing them. They get around their surroundings by placing their frontal suckers onto surfaces and then tugging their bodies in the direction they want to go. Their crawling is a lot like the inchworm's crawl. Leeches' bodies scrunch up and expand as they carry themselves across a space.
Although the classic swimming style of leeches is slow and relaxed, it isn't necessarily always that way. When leeches are annoyed or frightened by something, for example, they are more rapid and nimble in their motions.
If a leech detects that a host animal's body is getting closer, he might react by starting to crawl until, one way or another, his back sucker makes contact with the flesh and locks firmly into place. Leeches who live in the water do this especially frequently. When it comes to leeches on land, however, contact with a host is usually a happy coincidence.