Many people use “nightcrawler” and “earthworm” interchangeably, leading to confusion. Understanding the distinctions and connections between these terms clarifies their biological relationship and roles in ecosystems.
Understanding Earthworms
Earthworms are invertebrates belonging to the phylum Annelida, encompassing over 5,000 described species globally. They are recognized for their segmented bodies, lack of limbs, and burrowing habits in terrestrial environments.
Their bodies are muscular tubes with a digestive system running their entire length, processing ingested organic matter. Earthworms breathe through their moist skin, requiring a damp environment for survival.
The North American Nightcrawler
The organism commonly referred to as “the nightcrawler” in North America is scientifically known as Lumbricus terrestris. This species is thought to be native to Western Europe and has become widely distributed globally, often due to human introduction. Lumbricus terrestris is larger than many other earthworm species, typically reaching lengths of 110-200 millimeters (4.3-7.9 inches) and a diameter of about 7-10 millimeters (0.28-0.39 inches).
This species is reddish-brown. Nightcrawlers are known for their habit of emerging from their burrows at night, especially after rain or when dew is present, to feed on surface litter. This nocturnal activity contributes to their common name.
Distinguishing Features and Shared Benefits
North American nightcrawlers (Lumbricus terrestris) are a specific species of earthworm. All nightcrawlers are earthworms, but not all earthworms are nightcrawlers. The distinctions that often lead to separate common names include their size, with nightcrawlers being significantly larger than many other earthworm species. Their behavior also differs, as nightcrawlers create deep, permanent vertical burrows, emerging to the surface to feed, unlike some other earthworms that burrow horizontally or remain closer to the surface.
All earthworms, including nightcrawlers, provide benefits to soil health and ecosystems. They are considered “ecosystem engineers” due to their impact on soil properties. Earthworms improve soil structure by creating burrows, which enhances aeration and water infiltration, allowing oxygen and water to reach plant roots more easily. They also play a role in decomposition by consuming dead organic matter like leaves, breaking it down, and enriching the soil with nutrient-rich castings (feces). This process helps in nutrient cycling, making nutrients such as nitrogen, phosphorus, and potassium more available for plants.