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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 you see in the garden, compost or worm farm were most likely introduced to Australia.
Like all annelids, earthworms have tiny hairs on their surface called setae which help them to move underground.
They have a mouth at one end, and an anus at the other. You can tell which end of the earthworm is the head as it will be close to the clitellum.
Earthworms do not have lungs, and absorb oxygen through their skin. For this reason, earthworms need to be kept moist. Earthworms have both male and female body parts, but do not have any eyes or teeth.
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.
The head of the worm contains the mouth. It also has light and chemical sensitive organs to sense the surrounding environment.
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.
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.
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 your worm farm, 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 you usually see in your vegetable garden.
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 two metres deep.
All earthworms need their habitat to be slightly damp. This is because they don’t have skin like ours which keeps moisture in. They will dry out and die very quickly if they are not in a damp environment. If you pick up an earthworm in your hand, it will usually wriggle around because your skin has salt and other chemicals in it which will cause the worm to dry out.
Earthworms have tiny hairs on their bodies 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, 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 keep them from drying out.
How do earthworms move? | YouTube | Field of Mars EEC (0:22 min) | Video transcript
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, the red wigglers in our worm farms eat all the fruit and vegetable scraps from your lunches, as well as things like tea-bags, hair and even paper. They do not need to eat soil and they cannot eat things like orange peels or bread. They save us from having heaps of stinky bins of food waste that would have to go to land-fill, and they provide us with nutrient-rich fertiliser for our plants in return.
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.
Earthworms do so many important things for our planet. They 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 (which are called worm castings), they spread nutrients around in the soil. If you have a worm farm, you can collect worm castings and urine, store them in a bottle, and use it as free, organic (non-chemical) fertiliser for your plants. Some people call this mixture “worm tea” or “worm juice”.
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 about three weeks. They are a small version of an adult earthworm, there is no larval stage.
Earthworms are ready to breed when they are 2-3 months old.
If you have earthworms in a worm farm or compost, they can double their population in about three months. They can live up to 8 years old.
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.
This book was designed by teachers to support the NSW Science and Technology K-6 Syllabus and NSW English K-6 Syllabus.
Content supports living world, Australian animals and class studies on invertebrates.
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