Fisheries Research Report No. 1713, 1966

Michigan Department of Conservation
Research and Development Report No. 55
Institute for Fisheries Research Report No. 1713, 1966
Leeches

Clarence M. Taube

      Leeches are boneless, wormlike animals whose segmented bodies bear a suction structure at each end. The suckers are used for attachment; also, the one at the head end, which borders the mouth, assists in withdrawal of blood and juices from prey.
      Most of the leeches live in water. They are members of the phylum Annelida, which included earthworms. Four families occur in North America: the snail leeches (Glossiphoniidae), the fish leeches (Piscicolidae), the worm leeches (Erpobdellidae), and the blood suckers (Hirudinidae). Some 40 species have been recognized in the United States [14]. It is not known how many kinds inhabit Michigan but a publication [10] in which a complete listing was not attempted records 13 species.
      The adults of American leeches range from about ¼ inch to 12 inches in contracted length. Their colors are varied and usually subdued. The American medicinal leech, one of the larger and more familiar species in our state, is about 2 inches long, dark green on the back and reddish orange on the underside.
      Leeches may by found in various places in lakes, ponds, and streams, but they prefer soft-bottomed areas. They crawl around and rest on the bottom or else attach themselves to stones, logs, other submerged objects, and vegetation. The large kinds are adept swimmers.
      The foods of leeches differ according to species. The diet of the groups as a whole includes nonliving organic materials, tiny animals, and the blood and juices of snails, crustaceans, turtles, frogs, salamanders, and fishes.
      Leeches are produced from eggs. Although reproduction results from the mating of pairs, these animals are hermaphroditic; that is, each individual possesses both male and female sex organs. The earthworms also have this arrangement.
      Leeches are distributed all over the world. They inhabit the seas as well as fresh waters. Probably only the deserts and the continuously frozen areas of the polar regions lack these animals. Although most of them live in water, some exist on land and others are amphibious; the two latter groups are confined to the tropics.
      A good popular source of information on leeches is Ann Haven Morgan’s Field Book of Ponds and Streams [13]. Other good general accounts appear in The Encyclopedia Americana and The Encyclopedia Britannica. Serious students interested in the biology of these animals certainly should not overlook Mann’s scholarly book [9] on the subject.