Dick Warner: Invasive Australian flatworm leaves mixed feelings

When I discovered an Australian flatworm in my garden I had very mixed feelings, says Dick Warner. 

These invasive aliens are predators on earthworms and, after more than 30 years of careful organic gardening, I’m proud of my earthworms and rather protective of them.

However, my initial horror turned to doubt. We’ve heard so many atrocity stories over the years about invasive alien species and the impending disaster they are about to wreak on us but the end of the story is seldom ecological Armageddon. Then I thought of Aesop’s fable about the shepherd boy who cried wolf — it doesn’t have a happy ending.

The larger New Zealand flatworm does appear to have eradicated earthworms from parts of the North. However, the Australian species, which is much commoner than the New Zealand one in the Republic, has been around since the early 1980s and so far there are no reports I can find of it causing serious damage. There are native flatworm species, though they’re rather smaller, that also prey on earthworms and slugs but which appear to live in balance with their prey. Ecosystems have an amazing ability to adjust to the arrival of new species. It may take a little time but eventually the ecosystem digests the newcomer and a balance is achieved.

The truth of the matter is that a large proportion of our land animals and freshwater fish, and a slightly smaller proportion of our wild plants and birds, are aliens and our flora and fauna would be impoverished without them. We don’t lose sleep about the presence in our countryside of rabbits or pheasants or beech trees or tench. We do tend to worry a bit about more recent arrivals like grey squirrels, American mink, zebra mussels or Japanese knotweed. But the truth is that where I live grey squirrels are declining dramatically and the reds are making a slow comeback.

Mink numbers are also declining and they don’t seem to have affected the numbers of waterbirds. Most of the evidence I can find suggests that while zebra mussels have done some damage in our waterways this is outweighed by the good they’ve done by controlling algae growth and supplying a source of food for some fish and birds. And there is Japanese knotweed growing in some road verges around me but it doesn’t appear to be doing much damage and nobody is spending a fortune trying to eradicate it.

A cynical part of me suspects the hysteria that greets the discovery of a new invasive species may be artificially generated by biologists who have a great hunger for research grants. And I’m hoping, with crossed fingers touching wood, that this is the case with the Australian flatworms in my vegetable plot. But then I remember Aesop and the fact that eventually the wolf did come.


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