The Animal World

Earthworms: The Underground Helpers

Earthworms occur in large numbers in Europe, Asia and North America. They live in the soil and feed on the decomposing organic matter in it. They play an important role in humus formation: their excrement is an excellent fertiliser and they improve the air supply of the soil by loosening it. Their bodies consist of segments, which are apparent from outside, but certain internal organs are also repeated in the segments.

Clitellum

A thickened section of the body wall in earthworms playing an important role
in reproduction. It helps the pair to join during mating and it produces a mucous sac
in which the eggs are deposited.

Gastrointestinal tract

It consists of three sections: foregut, midgut and hindgut. It has two openings.

Circulatory system

Their closed circulatory system consists of the dorsal blood vessel, lateral vessels, the ventral blood vessel and the subneural blood vessels. Their red blood is pumped in the circulatory system by the contraction of the dorsal and lateral vessels.

gastrointestinal tract

Geographical range:
Europe, Asia, North America

Feeding behaviour: detritivore

Body length: 15–30 cm

Body mass: 2–10 g

Rings

Earthworms belong to the phylum
of Annelids. Earthworms´ bodies are segmented, that is, they consist
of a series of similar units. Arthropods are also segmented, but their segments are very different from each other
and form tagmata.

Properties

Their body is covered with moist skin, which plays a role in defence,
breathing and sensing light. It is also involved in movement, as it is fused
with the underlying muscle which
it uses for locomotion.

• Earthworms can be found in large numbers in humus-rich soil. The number of earthworms living in one hectare of forest soil can reach 3.5 million.

• They curl up to hibernate in winter at depths of 2 or 3 metres underground, either alone or in groups.

• During heavy rainfall, earthworms come to the surface due to lack of air underground.

• If earthworms are exposed to the Sun’s UV radiation, they die shortly afterwards.

• Although they lay many eggs, they cannot thrive every­where as they are preyed upon by many species in nature, such as hedgehogs, moles, shrews and birds.