Common Earthworm (Lumbricus terrestris): Nightcrawler Facts

What does a common earthworm look like?

The common earthworm has a long, cylindrical body divided into about 120 to 170 ring-shaped segments, most often 135 to 150. It is pinkish to reddish-brown, with the darkest color at the head end and paler tones toward the rear. The last part of the body is broad and flattened, which helps tell it apart from many other earthworms.

Mature worms carry a thick, raised band called the clitellum around segments 32 to 37. This “saddle” produces the cocoons that hold the eggs. Young worms have no clitellum, so a worm without one is not yet adult.

Every segment except the first and the last carries four pairs of tiny bristles called setae. They grip the soil and the walls of the burrow, which is why a nightcrawler can be so hard to pull out of the ground. At the front, a fleshy lip called the prostomium overhangs the mouth and is used to feel and taste the surroundings. Earthworms have no eyes, ears, legs, bones or lungs.

How big is a common earthworm?

Lumbricus terrestris is the largest earthworm that occurs naturally in much of Europe. A resting adult is usually 11–20 cm (4.3–8 in) long and 7–10 mm (0.3–0.4 in) thick, and it can stretch to about 25 cm (10 in) when fully extended. Mature worms reared in laboratories typically weigh about 4–6 g (0.14–0.21 oz), and well-fed worms can be heavier.

Earthworms of a given species keep roughly the same number of segments throughout life and grow by enlarging them. The nightcrawler is big by European standards but small next to giants such as the giant Gippsland earthworm of Australia, which commonly reaches about 1 m (3.3 ft).

Habitat and range

The common earthworm is thought to be native to western Europe and now lives across most of the continent. People have spread it to North America and many other temperate parts of the world, mostly by accident in soil and plant pots and later through the bait trade. In Britain it is called the lob worm, in Canada the dew worm, and in the United States the nightcrawler.

It thrives in permanent pasture, lawns, gardens, orchards, hedgerows and broadleaf woods with moist, fairly deep soil. It prefers neutral to slightly acidic ground and does poorly in fields that are plowed every year, where machinery injures it and there is little leaf litter to eat.

Soil scientists call it an anecic worm, meaning it lives in a permanent, vertical burrow and feeds at the surface. The burrow is lined with mucus and droppings and is used for months or years. Around the entrance the worm builds a small heap of leaf pieces and casts called a midden, which becomes a hotspot for fungi and tiny soil animals.

How earthworms move, breathe and sense

An earthworm has no skeleton. Its body cavity is filled with fluid and divided by walls between segments, forming a hydrostatic skeleton. Rings of circular muscle squeeze a segment to make it long and thin, and bands of longitudinal muscle shorten it and make it fat. Waves of these contractions pass along the body while the setae anchor it, pushing the worm forward through soil.

Earthworms breathe through their skin. Oxygen dissolves in the thin film of mucus that covers the body and passes into a dense net of blood vessels underneath, so the skin must stay moist. The red blood is pumped by five pairs of muscular vessels called aortic arches, explained in how many hearts an earthworm has.

A small brain sits above the throat in segment 3, joined to a nerve cord that runs along the belly. Giant nerve fibers in the cord allow a lightning-fast escape reflex that whips the worm back into its burrow. Light-sensitive cells in the skin warn it of daylight, and the whole body is very sensitive to vibration. Charles Darwin found that worms ignored loud notes from a bassoon, yet dived for cover when their pots were placed on a piano that was being played.

What do common earthworms eat?

The common earthworm is a detritivore, an animal that feeds on dead plant matter. At night it reaches out of its burrow, grips a fallen leaf with its mouth and drags it underground, often by the narrow tip. Leaves are left to soften with fungi and bacteria before being eaten. The worm prefers leaves rich in calcium and nitrogen, such as basswood, ash and aspen, and eats oak leaves less readily.

It also swallows soil, together with microbes, fungi and bits of dead animals and dung. Food passes through a muscular throat, a storage crop and a gizzard, where tiny grains of sand help grind it into a paste, before it is digested in the intestine. The waste comes out as casts, small heaps of crumbly soil that are richer in nutrients plants can use than the surrounding earth.

Behavior: life in a burrow

Common earthworms are most active on cool, damp nights. Warm nights and dry soil stop them feeding, and in hot summers they retreat to the deepest part of the burrow and become inactive. In mild, wet climates such as Britain’s they can stay active through much of the winter.

They come to the surface in larger numbers during and after heavy rain, but not to escape drowning; the reasons are explored in why worms come out when it rains. Even while feeding, a nightcrawler usually keeps its tail in the burrow, which is why birds and other predators often have to tug hard to pull one out.

Reproduction and life cycle

Each common earthworm is a hermaphrodite with both male and female organs, but it must mate with another worm. Mating takes place on the surface at night. Two neighbors lie belly to belly, head to tail, with their front ends overlapping and their tails still anchored in their own burrows, and each passes sperm to the other. Before mating, neighboring worms often visit each other’s burrows, and in one study they mated roughly every 7 to 11 days.

Sperm received from a partner is stored for up to about eight months. To lay eggs, the clitellum produces a band of mucus that the worm slides forward and off over its head, depositing its own eggs and the stored sperm inside. The band seals into a small, lemon-shaped cocoon, where fertilization happens, and the cocoon is left in the soil near the burrow. A worm can keep producing cocoons for up to a year after mating.

Young worms hatch fully formed after several weeks to a few months, depending on temperature, and have no larval stage. They live in shallow soil at first and only later dig deep vertical burrows. In the wild, common earthworms usually take more than a year to become mature.

Lifespan, predators and threats

How long common earthworms live in the wild is unknown. Individuals have survived about six years in captivity, but most wild worms are thought to die much younger.

Many animals eat them. Birds such as robins, blackbirds, thrushes, starlings, lapwings and gulls hunt them on lawns and fields; see how robins find worms. Moles, shrews, hedgehogs, foxes and the European badger, which in Britain feeds mainly on earthworms, are major mammal predators, along with toads, snakes, ground beetles and centipedes.

Along Europe’s Atlantic fringe, two flatworms accidentally introduced from New Zealand and Australia have wiped out common earthworms in some fields and gardens. Intensive plowing, soil compaction, acidifying fertilizers and some pesticides also reduce numbers on farmland.

Why the common earthworm matters

Darwin spent decades studying earthworms and described their work in his last book, published in 1881. He estimated that in parts of England worms brought more than 10 tons of dry soil per acre to the surface every year, slowly burying stones and old ruins. By burrowing, mixing soil and burying leaves, the common earthworm aerates the ground, helps rain soak in and recycles nutrients, as described in why earthworms are important.

Common earthworms as invaders in North America

The same habits cause harm where the species does not belong. In the northern United States and Canada, ice sheets wiped out earthworms during the last ice age, and for more than 10,000 years the forests grew without them. European earthworms arrived with settlers and spread along roads, gardens and lakeshores.

In hardwood forests around the Great Lakes, invasive worms, including the nightcrawler, can eat away the thick layer of fallen leaves on the forest floor. Native wildflowers, tree seedlings, salamanders and ground-nesting songbirds that depend on that layer have declined in heavily invaded woods. The common earthworm is therefore treated as an invasive species in parts of the north-central United States.

Conservation status

The common earthworm has not been assessed by the IUCN Red List and is listed as Not Evaluated. It remains abundant and widespread in Europe and in the many countries where it has been introduced. Local declines are linked to invasive flatworms and intensive farming, while in North American forests the concern runs the other way: stopping its further spread.