蚯蚓是对环节动物门寡毛纲类动物的通称。在科学分类中，它们属于单向蚓目。身体两侧对称，具有分节现象；没有骨骼，在体表覆盖一层具有色素的薄角质层。蛋白质含量达70%，还有微量元素，如磷、钙、铁、钾、锌、铜以及多种维生素。除了身体前两节之外，其余各节均具有刚毛。雌雄同体，异体受精，生殖时借由环带产生卵茧，繁殖下一代。目前已知蚯蚓有200多种，1837年被生物学家达尔文称之为地球上最有价值的动物。

循环系统是封闭式循环系统，消化管为一由前至后延伸的管状构造，排泄则经由肛门或肾管进行，喜食腐质的有机废弃物。以皮肤呼吸，会从背孔分泌黏液以保持皮肤的湿润。古人误以为蚯蚓出土时会发出声音。

The Lumbricidae are a family of earthworms which includes most of the earthworm species well-known to Europeans. About 33 lumbricid species have become naturalized around the world, but the bulk of the species are in the Holarctic region: from Canada (e.g. Bimastos lawrenceae on Vancouver Island) and the United States (e.g. Eisenoides carolinensis, Eisenoides lonnbergi and most Bimastos spp.) and throughout Eurasia to Japan (e.g. Eisenia japonica, E. koreana and Helodrilus hachiojii). An enigmatic species in Tasmania is Eophila eti. Currently, 670 valid species and subspecies in about 42 genera are recognized.