Places to Visit
School Veg Patch
There are about 25 species of earthworm found in Britain and of those about 10 can commonly be found in our gardens. The most common type can grow to about 30 cm (one foot) in length. Bet you thought that an earthworm was just an earthworm didn’t you? Most species are so difficult to tell apart that they don’t even have common names.
Earthworms belong to a group of animals called Annelida meaning ringed. Anyone who has looked closely at an earthworm will understand why this name is very appropriate as its body is made up of as many as 100 segments or rings. It is a soft-bodied creature having no skeleton.
Within the Annelida group the earthworm belongs to a sub group named Oligochaeta (quite a mouth full for such a simple creature). This name means “few bristles” describing the fact that the earthworm has four bristles on the underside of each of its segments. Using these bristles and the mucus it produces the earthworm can move across anything other than an extremely smooth surface where it cannot gain grip. The bristles on each segment are very strong. They can retract, (be pulled in), like the claws of a cat. You may have seen a blackbird tugging, trying to pull a worm out of the ground. The reason that this can be such a battle is because the bristles act as tiny hooks latching onto the sides of the worm’s tunnel. If the tail end of the worm breaks off in this struggle then the worm can regrow a new tail rather like a lizard can. Worms can sometimes regrow damaged parts, however it is not true that if you chop a worm in half it will divide into two separate worms. The head end may survive but it is more likely that the worm will die.
Photographs to come
If you look closely at a mature worm you will notice a thicker area of segments about a third of the way down from the head. You can see this clearly in the top photograph on the left.
People often think that this is a scar formed where a chopped worm has healed itself but this is not the case. This area is known as a saddle and is often a slightly different colour to the rest of the worm’s body. It is from this area that the worm produces the mucus, which eases its movements. The saddle also has another important function. It has an outer skin where five to fifteen eggs are deposited. Once the worm has mated this skin detaches and the worm wriggles backwards shrugging it off like a collar. Once free the collar seals and forms a cocoon in which the eggs are protected. Worms are hermaphrodite. This means that they have both male and female parts.
After mating both animals produce eggs. Young worms emerge from the cocoon between one and five months later.
If asked many people would probably guess that the worm’s tail is the pointed end, however this is not the case. The pointed end is the front end which helps the worm tunnel through the soil. Worms can exert quite a bit of power when tunnelling. Try holding a worm in your hand and then let it push between your closed fingers to feel how strong they are.
Earthworms don’t really have a true head. They have five hearts and no lungs. They have a very simple brain, the function of which is to control movement and not much else. Apparently if the worm’s brain is removed there is no noticeable change in its behaviour. The worm has no eyes or ears. It senses light along its whole body surface and if it is exposed to daylight it will quickly try to burrow back into the soil. Too much sunlight will kill it.
Blood flowing near the surface of a worm’s body gives it a pinkish brown colouring. As worms do not possess lungs they breathe by absorbing oxygen through their skin. If the ground becomes waterlogged then worms will drown and die as they will not be able to breathe.
Apparently captive worms (not sure why anyone would keep a pet worm), have been known to live as long as ten years but with the great number of predators on the look out for a tasty worm lunch it is unlikely that a ‘wild’ worm will live for anything like as long.
The greatest enemy of the worm is the mole as they share the same habitat. When a mole catches a worm it bites off the head so the worm can’t wriggle away and then the captive is stored underground in a sort of worm larder. Research suggests that a mole may eat up to 50 earthworms every day.
Other predators include many species of birds, shrews, amphibians, slow worms, hedgehogs, beetles, centipedes and even larger creatures such as foxes and badgers. If you see a blackbird walking across the ground cocking its head on one side it may be listening for the sound of a worm or other creature moving beneath the surface. It may also stamp on the ground, this sometimes fools the worms into thinking that it is raining and they come up nearer the surface and may even peak out of their tunnels to be grabbed by the cunning bird. If you hang washing out you may even notice earthworms venturing out of their holes underneath dripping washing.
Worms will leave their underground tunnels on warm damp night although they usually leave their tail end in their burrows so that they can retreat quickly if they are disturbed. Worms visit the surface and pull leaves down underground. They feed on dead grass and the tips of the leaves and drag the rest of the leaf into their tunnels as a lining. The leaves gradually rot, enriching the soil as they do so. Due to their love of decaying material, worms are found in great abundance in compost heaps or piles of manure.
It is probably true to say that if it wasn’t for the work of the earthworms then our soil wouldn’t be what it is today. Earthworms are found in most soils other than very sandy or acidic soil.
Worms improve soil aeration and stop it becoming compacted and stagnant. Their tunnels form an extensive system of ventilation shafts and drainage channels in the top nine inches or so of soil. During very cold weather earthworms can burrow several feet down into the ground. Some species also go into a rest phase during summer – a sort of summer version of hibernation. This is more accurately called aestivation.
Although earthworms will feed on roots or other parts of plants that have decayed, they do not feed on healthy plants. They mainly feed by swallowing soil and digesting any decaying plant or animal material within it. The soil passes through the worm and is then deposited in the form of worm casts. As worms can only digest very small particles of soil gradually the large particles and stones are buried deeper underground. Some types of worms deposit their casts on the surface, which can be unsightly on lawns. Many people collect the soil from worm casts to add to homemade growing compost. Other worms deposit their casts in the top layers of soil, bringing up minerals from lower down in the ground, which would otherwise be washed down away from plant roots. This is especially important in areas where little digging takes place. The worm casts contain higher levels of nitrogen, phosphorous and potassium than the surrounding soil. This 'fertilizer' is distributed throughout the soil. Research has shown that each worm can produce about 150g per year of free fertilizer. It may not seem very much unless multiplied by the number of worms likely to be in the soil. Opinion varies considerably on how many worms live in a square metre of soil but there seems to be a sort of consensus that it is about 200 depending on the type of land and soil.
In short an earthworm can be considered to be a gardener’s friend so try not to chop too many if half when digging.
Why not try making a wormery?