earthworms

Earthworms are terrestrial annelids in the phylum Annelida, commonly placed in the family Lumbricidae. They live in soils worldwide, burrowing to aerate the substrate and mix organic matter with minerals. By feeding on decaying leaves and other detritus, they contribute to decomposition and nutrient cycling. Sizes range from a few centimeters to about a meter in some tropical species; most prefer moist, temperate environments.

Anatomy and physiology: Earthworms have elongated, segmented bodies with a hydrostatic skeleton and external setae. They breathe through moist skin and lack gills. The digestive system includes a pharynx, esophagus, crop, gizzard, and intestine. The circulatory system is closed, with a dorsal vessel and five pairs of aortic arches; a ventral nerve cord and brain coordinate movement and responses. Most species possess a clitellum, a glandular ring involved in reproduction.

Reproduction and life cycle: Earthworms are hermaphroditic and typically mate by aligning ventrally and exchanging sperm. After mating, each worm secretes a mucus cocoon through the clitellum that contains eggs and stored sperm. The cocoon hatchlings develop directly into juvenile worms; there is no larval stage. Lifespan varies by species and conditions.

Ecology and human use: Earthworms play a key role in soil health by improving porosity, structure, and nutrient availability through casting. They are also used in vermicomposting, especially Eisenia fetida, to recycle organic waste.