Scientific Name: Lumbricus terrestris
In the concluding chapter of his book, 'The Formation Of Vegetable Mould, through the Action of Worms' (1881), Charles Darwin wrote:
"When we behold a wide, turf-covered expanse, we should remember that its smoothness, on which so much of its beauty depends, is mainly due to all the inequalities having been slowly levelled by worms. It is a marvellous reflection that the whole of the superficial mould over any such expanse has passed, and will again pass, every few years through the bodies of worms. The plough is one of the most ancient and most valuable of man's inventions; but long before he existed the land was in fact regularly ploughed, and still continues to be thus ploughed by earth-worms. It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organized creatures."
Where conditions are ideal with plenty of organic matter present, it is estimated that there can be up to 50,000 earthworms to the acre, and these will bring about 12 tons of material to the surface in a year.
They feed on partly decomposed organic matter in and on the soil, this is broken down further and after excretion the 'castings' are acted on by the soil micro-organisms. This means that the earthworm is an important part of the recycling of nutrients in the soil. In addition their burrowing aerates the soil and improves drainage, helping other soil organisms and plant roots.
The worm casts contain higher levels of nitrogen, phosphorous and potassium than the surrounding soil - the products of digested organic matter and trace elements brought up from deeper levels. Calcium carbonate is also added and this can make acid or alkaline soils more neutral. This 'fertilizer' is distributed throughout the soil and research has shown that each worm can produce about 150g per year - much better than a dry or granular fast-acting chemical fertilizer which has no humus, leaches away and may repel the worms. Some gardeners collect worm casts to use as a fertilizer and soil conditioner.
Recent studies have also found that enzymes excreted in the casts act as growth promoters on plants.
Earthworms usually dwell in the top few centimetres of the soil, but some species will go down nearly 2m. They need moisture as they absorb oxygen and give off carbon dioxide through their skin, so they burrow deeper if the soil dries out or freezes. However, they will drown in waterlogged soil so the increasing periods of prolonged wet conditions may harm the population - they are forced to the surface and birds exploit these conditions to make easy pickings of them. Usually they come to the soil surface at night when temperatures are lower and the humidity is higher - also the birds are not about, but badgers and foxes will be. Most soil types are suitable except very acidic conditions, and coarse sand.
They can reproduce when 3 - 6 weeks old, making a cocoon in the soil from which live worms emerge. They are hemaphrodites with male and female organs, but two worms have to join together to transfer sperm. This is done by sueezing under the structure commonly called the saddle which produces egg capsules, as in the picture below (real name the clitellum). Both eggs and sperm are deposited in a cocoon in the soil and live worms emerge after development takes place.
The cylindrical body is segmented and keeps its shape by fluid filled chambers. The common view that cutting a worm in half makes two is not true, some species can regenerate damaged segments at the rear end, so with such severe trauma both severed parts die. The front segment containing the mouth has an overhanging lobe, the prostomium, which can seal the mouth at rest, sense the surroundings and in some species is used to grip leaves to pull them into the burrow. Apart from the first and last segments there are several short hair-like bristles (setae) which grip the soil to allow movement.
Unfortunately the worm population of Northern Ireland and Co Down in particular, is under great threat at present from the New Zealand Flatworm. This interloper feeds exclusively on earthworms and can reduce the numbers to below detectable levels in the right conditions.
To increase the worm population, adding organic matter provides food and adding lime to acidic soil will help. They are said to like mint and planting it is supposed to attract them to the area. Turning over the soil too often has a detrimental effect, so the no-dig method of gardening is beneficial and they will do the incorporating of organic matter for you - this is part of the Permaculture technique of growing. The Brandling worms (Eisenia fetida) sold as fish bait are not suitable as they need the warmth of the wormery or compost heap.
Some people, usually those maintaining putting and bowling greens, do not welcome the worms because of their 'casts' which spoil the perfect playing surface they are trying to achieve. They can make the surface slippery as well and are the perfect medium for germinating weed seeds. A top-dressing of coarse sand has been shown to reduce the production of casts - I suppose they don't like eating sand or abrading their skin on it, any more than we do! An application of about 4cm split over three to four months should have some effect, ie. six or seven applications of 0.5cm every two weeks.
Where soil compaction is a problem on a playing field, earthworms have been brought in to improve the situation.
Earthworms are very important when recycling organic waste. They populate every compost heap and special wormeries or composting toilets mean we can keep all of the humus and nutrients for use at home. (Though you might have to watch out for animal welfare groups, recently in New Zealand a special study had to be carried out to see if the worms are traumatized by the ordeal, fortunately it was found that they are not.)
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