Worms

There are thousands of different species of Earthworm, but only 26 species live in the UK.  They have long been recognised for the benefits they bring to the environment and in Ancient Egypt, earthworms were considered so indispensable to the agricultural economy that Cleopatra supposedly declared the earthworm sacred, and any export of earthworms was subjected to the death penalty.

The importance of earthworm activity in our ecosystems can be ascribed to their characteristic burrowing activity, bringing subsoil to the surface, and the feeding strategy resulting in the mixing of both soil and organic matter. Thus, earthworms play a vital role in promoting soil oxygenation/aeration and in improving soil water relationships. By enhancing microbial activities earthworms aid in nutrient cycling processes and in soil structure development.

Earthworm Types

Of the 26 species found in the UK there are 3 main groupings :

Litter Dwellers - a species that inhabit the surface organic layers of the soil and may also occur within compost heaps. These include common species such as Eisenia fetida (the brandling or tiger worm) and Dendrobaena veneta (another striped worm).

Deep Burrowers – such as Lumbricus terrestris (the lob worm or common earthworm) and Aporrectodea longa (the black-headed worm) usually require a deep (up to 2m in depth), mature soil with a supply of surface organic matter.

Shallow Workers - such as Allolobophora chlorotica (the green worm) or Aporrectodea caliginosa (the grey worm) need less depth of soil and require a soil with a mixture of organic and inorganic components.

Earthworms are made up of many small segments known as 'annuli'. These annuli are ridged and covered in minute hairs that grip the soil allowing the worm to move as it contracts its muscles. At about a third of the worm's length is a smooth band known as the clitellum. The clitellum is responsible for secreting the sticky clear mucus that covers the worm. 

Life Cycle

There are 3 stages in the life cycle of an Earthworm :

COCOON – Earthworms are hermaphrodites but need to mate with other worms in order to exchange sperm.  Cocoons are created where eggs and sperm mix and 1-5 worms can be created in each cocoon which is yellowish in colour and smaller than a grain of rice. If the conditions are not good for hatching, such as too dry, these cocoons can remain dormant for years.
 
HATCHLING – In 2-3 weeks the new worms will emerge from the cocoon, they are ½ to 1 inch long and whitish in colour, almost transparent.  They are on their own from the outset and will mature in about 6 weeks.

ADULT – An Adult Earthworm is usually between 5-6 inches long, a cold blooded animal which needs to remain moist and is sensitive to light.  Earthworms avoid light and will become paralysed if exposed to it for too long. Most worms will eat as much as their own weight each day.

Benefits

The major benefits of earthworm activities to soil fertility can be summarized as:

Biologcal - The earthworm is essential to composting, the process of converting dead organic matter into rich humus, which is vital to the growth of healthy plants.  The cycle of fertility continues by the worm pulling down below any organic matter deposited on the soil surface (eg, leaf fall, manure, etc) either for food or when it needs to plug its burrow. Once in the burrow, the worm will shred the leaf and partially digest it, then mingle it with the earth by saturating it with intestinal secretions. Worm casts can contain 40% more humus than the top 6" of soil in which the worm is living.

Chemical - As well as dead organic matter, the earthworm also ingests any other soil particles that are small enough—including stones up to 1/20 of an inch (1.25mm).  Minute fragments of grit grind everything into a fine paste which is then digested in the stomach. When the worm excretes this in the form of casts on the surface or deeper in the soil, a perfectly balanced selection of minerals and plant nutrients is made available. Fresh earthworm casts are thought to be 5 times richer in nitrogen 7 times richer in phosphates and 11 times richer in potash than the surrounding upper 6 inches (150 mm) of soil. In conditions where there is plenty of available humus, the weight of casts produced may be greater than 4.5 kg (10 lb) per worm per year, in itself an indicator of why it pays the gardener to keep worm populations high.

Physical - By its burrowing actions, the earthworm is of great value in keeping the soil structure open, creating a multitude of channels which allow both aeration and drainage to occur. Thus the earthworm not only creates passages for air and water to traverse, but is itself a vital component in the living biosystem that is healthy soil

Avoiding Dangers

Earthworms are not dangerous in any way to humans and form part of the food chain for many species such as foxes, moles, birds and frogs.

Encouraging Earthworms

Avoid Spraying Chemical Fertilizers

The application of chemical fertilizers, sprays and dusts can have a disastrous effect on earthworm populations. Nitrogenous fertilizers tend to create acid conditions, which are fatal to the worms, and often dead specimens are to be found on the surface following the application of substances like DDT, lime sulphur and lead arsenate.

As earthworms are processors of large amounts of plant and mineral materials, even if not killed themselves they can accumulate pollutants such as DDT, lead, cadmium, and dioxins at levels up to 20 times higher than in the soil, which in turn are passed on at lethal dosages to the wildlife which feed upon them such as foxes, moles, birds and also frogs.


Feeding

Adding organic matter, preferably as a surface mulch, on a regular basis will not only provide them with their food and nutrient requirements, but also creates the optimum conditions of heat (cooler in summer and warmer in winter) and moisture to stimulate their activity.

Interesting Facts


A Threat to the Earthworms

A recent threat to earthworm populations in the UK is the New Zealand Flatworm (Artiposthia triangulata), which feeds upon the earthworm and has no natural predator. At present sightings of the New Zealand flatworm have been mainly in Scotland and parts of Northern England.  This is no reason for complacency as it has spread extensively since its introduction in 1960 through contaminated soil and plant pots. Any sightings of the flatworm should be reported to the Scottish Crop Research Institute, who are monitoring its spread.


Why do Earthworms rise to the surface when it rains?

It has been suggested that earthworms use the moist conditions during periods of rain to migrate over the soil surface more quickly than traveling underground.


If you cut an earthworm in half do both bits survive?

Usually if you cut an adult earthworm in half the head end (the bit with the saddle) may survive but the tail end eventually dies when food resources are exhausted (It may continue to wiggle for some time).