Earthworms Spread by Human Activity
Worms Improve Soil Fertility but Invasive Species do Damage
Jun 23, 2009
Charles Darwin thought that there were over 50,000 worms per acre of good farmland, but more recent research shows that there are more than five times that number. In really fertile land (in the U.K.) there can be more than a million (over 400 per square metre).
Earthworms and Soil
Worms improve the soil and improve fertility in several ways:
- By dragging leaves and other vegetable material underground where it is broken down and adds humus,
- By making thousands of tunnels which allow air to penetrate and facilitate efficient drainage,
- By ejecting their waste (as ‘worm casts’) at the surface. This is finely ground mixture is much richer in nitrates and phosphates than the surrounding soil, and each worm can produce about 10 lb of it per year!
Wormeries and Vermicomposting
- Some species of worm (notably ‘Red Wigglers’ – Eisenia foetida and E. andrei) will happily feed in vegetable waste. They do not live in the soil, but in piles of rotting material and compost heaps.
- Wormeries, large and small, allow rapid conversion of many types of organic waste into useful garden fertiliser (vermicomposting).
- Wormeries can also be used to raise worms as bait for fishermen, but worms for this trade can also be harvested in a much more amusing way – by ‘grunting’ for them!
Grunting for Worms
A few people make their living by ‘Grunting for Worms’ – driving a stake into the ground and then rubbing it to produce vibrations that cause the worms to come up to the surface.
These worms are sold as fishing bait, and sometimes fishermen leave surplus bait where they have been fishing. (This is one of the ways in which novel worm species can be introduced into new habitats.)
Invasive Worm Species and Ecological Problems
Worms get moved from place to place when construction workers import soil, when pot-plants are put in the garden, and when fishermen throw away the worms they did not use as bait after a day of fishing.
In the U.S.A. about a third of the worm species have been introduced from elsewhere and are ‘invasive species’.
Worms are generally known to be a ‘good thing’, and many people do not realise that these invasive species can wreak havoc in certain environments. A couple of examples:
- Some forests, and the plants that are found in them, need a deep layer of undisturbed leaf litter. New species of worm can rapidly remove this litter, permanently altering the habitat.
- A new earthworm species might be great food for adult salamanders, but too big for the young to tackle.
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