The common “nightcrawler” most people encounter is the European or Canadian Nightcrawler, scientifically known as Lumbricus terrestris. This species is widely recognized due to its popularity as fishing bait and its habit of emerging from the soil at night. When fully grown and extended, a typical L. terrestris specimen reaches a length between 20 to 25 centimeters (about 8 to 10 inches). The maximum weight for this common worm falls within the range of 5 to 40 grams.
The Standard Nightcrawler’s Maximum Size
Lumbricus terrestris is the largest and most familiar nightcrawler. While the typical maximum length is 25 centimeters, exceptional individuals have been recorded reaching up to 35 centimeters when fully stretched. This length is often exaggerated in casual observation because the worm’s body can expand and contract significantly as it moves.
The girth of a mature nightcrawler typically measures between 7 to 10 millimeters in diameter. This size allows it to establish deep, semi-permanent vertical burrows, classifying it as an anecic earthworm. The weight of an adult L. terrestris rarely exceeds 40 grams. This large size is why it is valued as angling bait.
Species Confusion and Record Holders
The term “nightcrawler” is often used loosely, leading to confusion with other much larger earthworms globally. For example, the African Nightcrawler (Eudrilus eugeniae) is frequently used in vermicomposting and for bait, commonly growing to lengths over 15 centimeters (six inches). While substantial, this African species is still dwarfed by truly giant earthworms.
The Australian Giant Gippsland Earthworm, Megascolides australis, is one of the most famous examples of extreme size. This species averages about 1 meter (3.3 feet) in length and 2 centimeters in diameter, with some recorded specimens reaching up to 3 meters (nearly 10 feet). These giants can weigh as much as 400 grams. However, the absolute record belongs to a South African species, Microchaetus rappi, with a specimen once measured at a staggering 6.7 meters (21 feet) long.
Environmental Factors Influencing Growth
A nightcrawler’s size is heavily influenced by the conditions of its habitat, not solely by its genetics. To reach maximum potential, a worm requires a consistently hospitable environment that minimizes stress and maximizes resource availability. Soil organic matter is the primary food source, and a high density of decaying plant material, such as leaf litter, directly supports increased growth.
Moisture levels are a significant factor, as earthworms breathe through their skin and require constant dampness to survive and move efficiently. Optimal growth occurs in moist, but not waterlogged, soil conditions; drought is a major limiting factor that slows activity and growth. Temperature also plays a role, with growth rates increasing within the optimal range, while extreme cold or heat can halt development or be lethal.
The soil’s chemical properties, particularly pH, also affect growth, with most common nightcrawlers preferring neutral to slightly acidic soil conditions. When these external factors—food, moisture, temperature, and pH—are all within the ideal range, the nightcrawler is able to achieve its maximum size. Soil texture, with light to medium loams being favored, also contributes to ease of movement and burrowing, which indirectly supports growth.