The use of the worm, which reaches a maximum length of 3mm, has been patented by scientists at Bristol University's Long Ashton research station. The worm, called Phasmarhabditis sp., belongs to the family of nematodes, or roundworms.
Dr David Glen and Dr Michael Wilson, scientists at Long Ashton, set out to find a means of controlling slugs that cause enormous damage to winter wheat. When winter wheat grows in the spring, farmers often find large bare patches caused by slugs, which eat the seed.
The two scientists trapped slugs in the fields around Long Ashton and kept them in overcrowded conditions so that any infected agent would have the best chance of multiplying. Before long, the slugs began to thicken and shrivel, and the scientists, to their surprise, found a worm was responsible. They had expected to find a bacterium, virus or fungus.
After almost three years of experimental work involving a variety of crops, the Long Ashton scientists have been able to show that soil sprayed with the worms gives a much higher than average yield of crops. They are now well on the way to developing a technique that will allow the worms to be sold commercially.
The worms are grown artificially by the billion in vats and are fed on liquid food. They are then mixed with clay, which acts as a carrier, and can then be kept under refrigeration for several months before being mixed with water and then sprayed on the earth.
The patent worms are being marketed by Agricultural Genetics Company, of Cambridge, which sells similar live-worm mixtures to control black vine weavel, a common pest of house plants, and a fly that attacks mushrooms.
There is no danger of the nematode worm infecting human beings. It cannot survive at temperatures above 25 C and would quickly die if accidentally swallowed.
The worm has important advantages over chemical pesticides, which kill animals that are beneficial to the soil, such as earthworms, beetles and sometimes birds. The worm, however, will only kill slugs. It is partial to the small grey field slug, Deroceras reticulatum, but will also attack the large black garden slug, Arion ater, and others.
'This is an important economic development for farmers and growers,' Dr Glen said. 'But we believe it will also be useful to gardeners.'