Wanted, dead or alive: flatworms

Earthworms are under threat from an imported cousin.

Flatworms could be a really serious pest and without doubt Britain's gardeners are to blame." Manchester University's Hugh Jones is blunt as he describes the arrival and spread of the latest menace to threaten our flora.

He is referring to the alien worm which is destroying our native earthworm population. The dark-brown invader was first discovered some 30 years ago in Belfast gardens and identified in London's Natural History Museum as Artioposthia triangulata, a native of New Zealand's South Island beech forests. This small, ribbon-like creature almost certainly travelled half way around the globe as a stowaway in the soil of pot plants.

When motionless the flatworm is just 2-3in long, but this changes to 6-8in as it moves along - and it is capable of squeezing through the thinnest gap (one report details an escape through the knot of a tied up polythene bag). It feeds by enveloping a hapless earthworm with its body and secreting copious amounts of slime laden with digestive enzymes. This reduces the unfortunate victim to a soup which the predator then drinks through a mouth in its underside.

This has worrying implications for farmers and gardeners alike. Earthworms are an essential part of fertility in many areas, particularly in wet or thin soil unsuitable for ploughing. "Earthworms are vital to drainage - particularly the top 6-9in of soil," says Dr Jones. "Without them many naturally damp pastures would revert to marshland."

In addition, earthworms drag nutrients down from the surface and aerate the soil. Many plants use their tunnels as an easy way of extending their root systems. As a result, there is a clear correlation between worm numbers and plant growth.

Flatworms upset this delicate balance as they literally drink their way through our native species. Researchers in Northern Ireland have discovered that under ideal conditions, a flatworm eats 14 worms a week but if the supply dries up, rather than starving or moving to pastures new, it will simply stop eating. Apparently flatworms can survive for a year without food by reducing their reproduction and slowly absorbing their own tissue.

One of the major problems tackling the menace is that very little is known about the flatworm - both here and in its native environment. Hugh Jones, for example says the new species are being discovered almost weekly in its native habitat and as a result he is uncertain of the identity of a second British invader. "We think it is Caenoplana alba, but we are waiting until Australian taxonomists finish detailing their native species before we can be sure," he says. For the time being, he and his fellow researchers refer to it as the "pink un".

Unlike its New Zealand cousin, the second species has spread north from an origin in southern Britain. Fortunately, being rather smaller, it appears less harmful to biggest native worms. But it is a worry nevertheless.

Derek Cosens, a senior lecturer at Edinburgh University, says this is typical of virtually every aspect of our knowledge. Although one of Britain's leading flatworm experts, he admits that his research is based mainly on project work done by his final year undergraduates. Dr Cosens believes the worms depend on cold, wet and damp conditions and are thus likely remain confined to the west and north of Britain.

The flatworm seems to have almost no predators but some preliminary research in Edinburgh now suggests a so-far unidentified beetle may eat the invader. "What we really need is funding for a post-gradutate to do a thesis," says Dr Cosens. "That would revolutionise our understanding."

In the meantime, what do you do if you find your garden has been invaded by flatworms? Dr Jones at Manchester University says that to kill a flatworm you sprinkle salt on it or drop in jam jar of water or vinegar. And if you want to help find a remedy to flatworms you could start by sending him your samples. Put them in a small sealed pot with a bit of damp tissue and address your package to Dr Hugh Jones, 3239 Stopford Buildings, University of Manchester, Manchester M13 9PT.