Earthworms

What are earthworms?

Earthworms are a type of invertebrate, which means they do not have an internal skeleton. They belong to a group of invertebrates called  annelids. All annelids are divided into segments. The term annelid comes from the Latin word for ‘little ring’.

There are about 6000 different species of earthworm and about 1000 of these are native to Australia. The worms in the garden, compost or worm farm were most likely introduced to Australia.

Earthworms are divided into parts called segments.

What are the features of earthworms?

Earthworms have a mouth at one end and an anus at the other. They have both male and female body parts. Earthworms do not have lungs and absorb oxygen through their skin. For this reason, earthworms need to be kept moist.

Earthworms usually reach sizes up to 10 centimetres long but the Gippsland Giant Worm,  Megascolides australis,  can grow up to 3 metres long. They live in a small area in Victoria in Australia and unfortunately there are not many left.

Head

The head of an earthworm is the end close to the clitellum, the wide band. The head of the worm contains the mouth. It also has light and chemical sensitive organs to sense the surrounding environment. Earthworms do not have eyes or teeth.

Clitellum

The clitellum is sometimes called a saddle. The clitellum contains the gland cells. These cells are used to create a cocoon or egg that holds the worm embryos.

Segments

Earthworms have between 100 to 150 segments. Each segment contains muscles that help the worm to move. Each segment has bristle-like hairs called setae which grip the soil to help with movement.

Where do earthworms live?

There are three different types of earthworms that live in slightly different habitats. Some earthworms just inhabit the top layer of  leaf litter  or compost and do not burrow down into soil. These worms are the ones that live in worm farms, for example, a red wiggler worm.

Other types of worms live in the top layer of soil and eat and burrow there. These are the worms usually seen in vegetable gardens.

The third type of earthworm digs permanent burrows deep into the soil and comes to the surface to eat. The burrows can be up to 2 metres deep.

All earthworms need their habitat to be slightly damp. Because earthworms absorb oxygen through their skin, they need to be kept moist. They will dry out and die very quickly if they are not in a damp environment. If a person picks up an earthworm in their hand, it will usually wriggle around because human skin has salt and other chemicals in it which will cause the worm to dry out.

Earthworms live in the soil.

How do earthworms move when they don’t have any legs?

Like all annelids, earthworms have tiny hairs on their surface called setae which they can use to anchor themselves in the soil to help pull themselves along. They contract and stretch the sections of their bodies, a bit like a slinky toy, which causes them to move forward. Earthworms can squeeze mucus out of their bodies which makes them slide more easily as well as helping to prevent them from drying out.

What do earthworms eat?

Earthworms are decomposers. They eat organic matter such as leaves and food scraps and some eat soil which helps them to digest their food.

At the Field of Mars Environmental Eduincation Centre, the red wigglers in the centre's worm farms eat all the fruit and vegetable scraps from student lunches as well as things like tea-bags, hair and even paper. Red wrigglers do not need to eat soil and cannot eat things like orange peels or bread. Worm farms process organic food waste and provide with nutrient-rich fertiliser for plants in return.

What eats earthworms?

Earthworms are a very important source of food for other animals such as bigger invertebrates, birds, reptiles and mammals. To avoid becoming food, earthworms spend most of their life under the ground or under a log, rock or leaves.

How do earthworms benefit ecosystems?

Earthworms break down organic matter such as leaves and fruit and vegetable scraps into fertile compost which is important for plants to grow well.

When earthworms burrow underground they create little tunnels that help oxygen and water reach the roots of plants.

When earthworms excrete, called worm castings, they spread nutrients around in the soil. Worm castings and urine can be collected from worm farms, stored in bottles and used as free, organic fertiliser for plants. Some people call this mixture 'worm tea' or 'worm juice'.

Earthworms will feed on decaying leaves in leaf litter.

What is the life cycle of earthworms?

Earthworms have both male and female reproductive organs but still need another worm to reproduce.

They start their life in an egg-cocoon which contains an average of four young. The babies hatch after 3 weeks. They are a small version of an adult earthworm as there is no larval stage.

Earthworms are ready to breed when they are 2 to 3 months old. In a worm farm or compost bin can double their population in 3 months.

Earthworms can live up to 8 years old.

Even though earthworms have both male and female reproductive organs they still need another worm to reproduce.

Invertebrate explorer digital book

Find out more

Written by teachers, the Invertebrate Explorer digital book explores the incredible world of Australian invertebrates.

Students can use the book to investigate classification, features, adaptations and habitats of a variety of Australian invertebrates through narrated videos, stunning images, interactive activities and detailed text.

Content supports living world, Australian animals and class studies on invertebrates.

Download free from Apple Books