Potworms

Enchytraeidae is a family of microdrile oligochaetes. They resemble small earthworms and include both terrestrial species known as potworms that live in highly organic terrestrial environments, as well as some that are marine. More than 700 species in about 30 genera have been described worldwide, although the true diversity of the family is thought to be much higher. Most species are small, whitish or transparent worms only a few millimetres long that feed on decaying organic matter and the microorganisms colonizing it, making them important contributors to decomposition and nutrient cycling in soils. The peculiar genus Mesenchytraeus is known as "ice worms", as they spend the majority of their lives within glaciers, only rising to the surface at certain points in the summer. Enchytraeidae also includes the Grindal worm (Enchytraeus buchholzi), which is commercially bred as aquarium fish food. Certain varieties of Enchytraeidae are partially responsible for the notorious "dark earth" archaeological layers in post-Roman Era British urban centers such as London.

Enchytraeids, like earthworms, are ecosystem engineers, influencing the soil structure by creating aggregates of various sizes. Negative interactions between potworms and earthworms have been experimentally registered, and observed in the field when a wide array of Land use types were considered. They could be explained by different environmental optima, e.g. microclimate, pH, texture, nutrient availability, potentially reinforced by antagonisms and exploitative competition. Enchytraeids are less sensitive than earthworms to agricultural intensification and replace them in soils with heavy pesticide use. However, positive interactions between these two oligochaete groups have also been observed in microcosm experiments. Enchytraeids have been shown to feed on earthworm excrements (earthworm casts) which they pulverize and transform into fluffy masses of their own excrements (enchytraeid faeces), which form the bulk of Moder humus OH horizons.