Earthworms, members of the genus Lumbricus, are often thought of as the motivation for awakening birds and as the favored bait of the young angler. The night crawler (Lumbricus terrestris), introduced to North America by early European settlers, is an earthworm that ranges from 90 millimeters up to 300 millimeters in length and constructs burrows up to 2.5 meters (approximately 8 feet) in depth.

As the night crawler burrows in the earth, ingesting mud and vegetational litter, it removes turret-like structures (middens) that mound up at the entrances and exits of the earthen tunnels. Organic home gardeners seek the middens as a rich source of minerals and organic matter for their vegetable and flower gardens, and a commercial product is marketed. As the detritivorous nightcrawler ingests and eliminates mineral and organic matter, it is aerating and turning over the soil, making plant growth easier and more productive. In terms of animal biomass per hectare in terrestrial ecosystems, night crawlers hold the record, with densities of up to 70 per square meter of lawn or prairie.

Typically, night crawlers will mature in a year and live up to 6 years. With obligate sexual reproduction in these hermaphroditic annelids, an average of 38 cocoons per year is produced by each individual. If conditions are suitable, colonies of Lumbricus expand about 3 to 5 meters per year.