Earthworms are often perceived as small, unassuming creatures beneath our feet. While many familiar species fit this description, the diversity within the earthworm family is vast, encompassing some truly immense invertebrates. The size of an earthworm can vary dramatically, from a few centimeters to several meters.
Record-Breaking Giants
Among the most prominent is the Giant Gippsland Earthworm (Megascolides australis), native to the Gippsland region of Victoria, Australia. These impressive annelids average about 1 meter (3.3 feet) in length and 2 centimeters (0.79 inches) in diameter, with some individuals capable of stretching up to 3 meters (9.8 feet) long. Adults typically weigh around 200 grams (0.44 pounds), though some reach 400 grams. They inhabit deep burrow systems in blue, grey, or red clay soils along stream banks and hillsides, requiring high soil moisture. They mature slowly, taking approximately five years to reach their full adult size.
Another remarkable giant is the African Giant Earthworm (Microchaetus rappi), found in the Cape region of South Africa. This species averages 1.4 meters (4.6 feet) in length, with some specimens recorded up to 6.7 meters (22 feet) and weighing over 1.5 kilograms (3.3 pounds). These colossal worms are known to surface after heavy rains, making them occasionally visible despite their subterranean lifestyle.
Factors Influencing Size
The considerable variation in earthworm size stems from a combination of biological and environmental factors. Different earthworm species possess distinct genetic predispositions for growth. Beyond species-specific traits, an earthworm’s age plays a role, as these invertebrates continue to grow throughout their lifespan, with older individuals generally achieving greater sizes.
Environmental conditions significantly influence how large an earthworm can become. A rich habitat with abundant organic matter (decaying plants, fungi, bacteria) provides necessary nutrients for substantial growth. Soils with high-quality food resources, like manure and legume residues, benefit earthworm populations.
Temperature and moisture levels also determine size. Earthworms require moist soils to prevent dehydration, as water constitutes over 75% of their body weight. Optimal temperatures (32-86°F) promote faster growth and activity. Soil properties like pH, nutrient content, and organic matter also contribute to habitat suitability, influencing earthworm size and health. Silty soils with high water retention and organic matter content create an ideal environment for earthworm development.
Common Earthworm Dimensions
While the record-breaking giants are impressive, most people encounter much smaller earthworm species in their daily lives. The common earthworm, Lumbricus terrestris, often referred to as the nightcrawler, is a familiar sight in gardens and agricultural fields across temperate regions. These worms measure 20 to 25 centimeters (7.9 to 9.8 inches) when fully extended. Their diameter ranges from 7 to 10 millimeters (0.28 to 0.39 inches), and they can weigh 5 to 40 grams. Lumbricus terrestris is a deep-burrowing species, creating permanent vertical tunnels in the soil.
Another frequently encountered species, especially in compost bins, is Eisenia fetida, commonly known as the redworm or red wiggler. These smaller worms are well-adapted to decaying organic material and thrive in environments rich in compost and manure. Eisenia fetida reaches an overall length of 3 to 13 centimeters (1.18 to 5.12 inches) and has a slender diameter of 3 to 5 millimeters (0.12 to 0.2 inches). An average redworm weighs approximately 4 to 6 grams. Unlike deep-burrowing species, Eisenia fetida primarily inhabits the surface layers of soil, where decomposing organic matter is abundant.