Ball of live aquatic oligochaetes (Oligochaeta, Family Tubificidae); © P.M. Chapman, EVS Consultants.

Pristina leidyi Smith, 1896 (Oligochaeta, Tubificidae, Naidinae*); © S.J. Taylor & M.J. Wetzel, INHS.

Oligochaetology is the study of worms - specifically, the Class Oligochaeta within the Phylum Annelida. As of 31 March 2006, over 8,400 species of oligochaetes representing 38 families, 812 genera, and 62 subgenera had been described worldwide; approximately 5,000 of these are considered valid today. In just the past 12 years, two families, 72 genera, 21 subgenera, and 1,450 species have been described as new to science.

Other groups in the Phylum Annelida -- the true segmented worms -- include the Acanthobdellida (bristle worms), Aeolosomatida (suction-feeding worms, now considered to be a group within the Polychaeta), Branchiobdellida (crayfish worms), Hirudinea (leeches), Polychaeta (sand worms, tube worms, and clam worms), and Parvidrilidae (a new family of annelids closely related to the Oligochaeta). Over 15,000 species of annelid worms have been described worldwide; we now recognize 2,450 species in North America north of Mexico.

Annelid worms occur in virtually all habitats where water is present, even in areas that are only slightly moist. Numerous species also occur exclusively on land. Most annelids are free-living, but several species have symbiotic (commensal, mutualistic, parasitic) relationships with other animals and plants during part of, or throughout, their life cycle.

Aquatic oligochaete worms (aquatic oligochaetes, microdriles).
Aquatic oligochaete worms are an important and often dominant group in aquatic systems, providing a valuable food source for many other aquatic organisms. Aristotle (384-322 BCE) was perhaps the earliest person in history to recognize that aquatic worms have the ability to thrive in organically polluted waters, often forming dense colonies that resemble red waving carpets. Recent works have noted the presence of aquatic worms in almost every habitat that is associated with water, including pristine springs, streams, wells, seeps, hyporheic (subsurface, groundwater) habitats, and lakes, as well as large rivers, freshwater and marine harbors, and even waste retention ponds negatively influenced by domestic and industrial discharges.

Terrestrial oligochaete worms (earthworms, megadriles, nightcrawlers).
Earthworms play an important role in the decomposition of organic matter, mineral cycling, and the aeration, drainage, and root penetration of the soil; through this activity, they also provide suitable habitat for smaller soil fauna, particularly micro-organisms. It has been estimated that earthworms can 'move' up to 18 tons of soil per acre each year. Abundance estimates of earthworms have been as high as three million per acre.

Charles Darwin (1809-1882) was a British naturalist well-known throughout the scientific and lay communities for his voyage to the Galapagos Islands and elsewhere in the world on the HMS Beagle, his theories on evolution, the origin of species, natural selection, and the descent of Man. Perhaps a lesser known fact about Darwin, however, was his career-long dedication to the study of earthworms -- cultivating and enumerating earthworm communities in clay pots and even playing piano for them to confirm his suspicions that worms are deaf. The final book published by Charles Darwin in 1881, entitled "The formation of vegetable mould, through the action of worms, with observations on their habits" included a quote that emphasized his respect of earthworms: "It will be difficult to deny the probability that every particle of earth forming the bed from which . . . old pasture land springs has passed through the intestines of worms."

Currently, 161 species of terrestrial oligochaetes occur in North America; of these, 116 are considered native, and 45 are considered to have been introduced from other countries (Reynolds & Wetzel 2004).

I especially encourage you to visit the Discover Life in America, Inc. (DLIA) website; there you will find contact information for scientists associated with the various taxonomic working groups (TWIGS), volunteers already contributing to this project, the administrative and scientific staff of DLIA, and a variety of opportunities for public involvement in research and education in the Park. Please Note: The new DLIA / ATBI websites currently are being reorganized; information is being updated and transferred from websites hosted previously at other institutions, so please check regularly.

Thank you for your interest! Your suggestions for / comments on this research and on the content of webpages associated with this website are encouraged. Please forward them to me via *E-Mail: mjwetzel{AT}uiuc.edu
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