The terms “earthworm” and “nightcrawler” are frequently used interchangeably, causing confusion. “Earthworm” represents a broad category of segmented worms, while “nightcrawler” refers to a specific type within that group. This article clarifies the relationship between earthworms and nightcrawlers.
Understanding Earthworms
“Earthworm” is a general term for thousands of segmented worm species belonging to the phylum Annelida and the class Oligochaeta. They have cylindrical bodies divided into numerous ring-like segments. Earthworms vary in size, color, and behavior, found globally in diverse habitats including soil, freshwater, and some marine environments.
They play a key role in soil health and nutrient cycling. Earthworms consume decomposing organic matter, like dead leaves, and excrete nutrient-rich castings that improve soil fertility. Their burrowing creates tunnels within the soil, enhancing aeration and water infiltration. This prevents soil compaction and supports healthy plant roots.
Meet the Nightcrawlers
The term “nightcrawler” is a common name for Lumbricus terrestris, a specific, large earthworm species. It is often called the Canadian Nightcrawler in North America due to commercial harvesting from Southern Ontario. Other large earthworm species, such as African or European Nightcrawlers (Eisenia hortensis), are also sometimes called nightcrawlers, but Lumbricus terrestris is the most recognized.
Lumbricus terrestris is a large, reddish-brown worm, often reaching 20 to 25 centimeters when extended. They emerge from burrows to the soil surface at night, especially during damp conditions, to feed and mate. During the day, they retreat into deep, vertical burrows. This species is native to Western Europe but has become widely distributed globally.
Key Distinctions
While all nightcrawlers are earthworms, not all earthworms are nightcrawlers; Lumbricus terrestris possesses distinct traits that set it apart from many other common earthworm species. Nightcrawlers are larger and thicker than many other earthworms, such as the smaller red wigglers (Eisenia fetida). Lumbricus terrestris can weigh between 5 to 40 grams and measure up to 25 cm in length, whereas red wigglers are much smaller.
Their burrowing habits also differ. Lumbricus terrestris creates deep, permanent vertical burrows that can extend several meters into the soil, often returning to the same burrow. In contrast, many other earthworm species, like red wigglers, tend to create shallower, more extensive horizontal tunnels closer to the surface. This deep burrowing by nightcrawlers improves soil aeration and drainage.
Nightcrawlers primarily feed on organic matter found on the soil surface, pulling leaves and other plant debris down into their burrows. This anecic (deep-burrowing) feeding strategy contrasts with many other earthworms that consume organic matter directly within the soil itself. Nightcrawlers are also hermaphrodites, meaning each individual possesses both male and female reproductive organs, and they mate on the soil surface, exchanging sperm. After mating, they produce cocoons containing eggs, with fertilization occurring within the cocoon.
Nightcrawlers are commonly used as fishing bait due to their large size, durability, and lively movement. This differs from smaller earthworms, such as red wigglers, which are more frequently used for vermicomposting (composting with worms) due to their voracious appetite for kitchen scraps and rapid reproduction rates.