Sandy’s Garden ... Flatworms are Back

Sandy Simpson
Sandy Simpson

Well, strictly, flatworms are back in the public eye.

These unwanted immigrants from New Zealand have never actually gone away since they were first found in the UK near Belfast as long ago as 1963. Arthurdendyus triangulatus, to give this alien its proper botanical name, is named after Arthur Dendy, a zoologist who was born in 1865 at Manchester. After graduating in 1885 with an honours degree in zoology, Dendy held several appointments in this country before he was appointed demonstrator and assistant lecturer in biology at the University of Melbourne. In 1893, Dendy was appointed Professor of Biology at Canterbury College, University of New Zealand, where he continued his ground-breaking research into land planarians … flatworms … the creatures which are named in his honour. In 1903 he was appointed Professor of Biology at the University of Cape Town, South Africa, moving to become Professor of Zoology at King’s College, London just two years later. He died in King’s College Hospital in 1925 at the relatively young age of 60.

But these details, taken from the Australian Dictionary of Biography, tell us nothing of the habits of the New Zealand flatworm which, after making its first UK appearance in Northern Ireland, is now widespread throughout the UK, its Scottish stronghold being in the populated central belt from Glasgow to Edinburgh. The species is harmful because it eats earthworms, thus reducing soil fertility and lowering the population of earthworm-feeding wildlife. The flatworm likes to shelter under debris on the surface of soil in gardens and on the edges of areas of agricultural land; and this trait, allied to its sticky body, has led to flatworms being inadvertently spread in containerised plants, in compost and on pets.

Athur Dendy actually tasted flatworms in a bid to discover why they seem to have few natural predators even in their home country; and he found their taste to be “an exceedingly unpleasant sensation”. Rather him than me! The flatworms’ liking for eating our native worms results in a reduction in earthworm activity, which in turn limits plant growth – a serious and costly matter for arable farmers. I learn from the website of the Centre for Agriculture and Biosciences International (CABI) that, “A flatworm-induced reduction in earthworm populations could change soil structure and hydrology leading to poor soil drainage. There is evidence of a build-up of dead organic matter on the soil surface at flatworm-infested sites.” Unsurprisingly, given the financial damage done to the agricultural industry … estimated at many millions of pounds annually in Scotland alone … The Wildlife and Natural Environment Act (Scotland) 2011 forbids the intentional distribution of New Zealand flatworms. And, gentle reader, should you wonder why anyone would wish to spread these pests, there are unsubstantiated tales of bowling green and golf course groundsmen doing this very thing to reduce earthworm casts on their lovingly-cultivated sward.

The gardener may be alerted to the possible presence of flatworms by noticing smaller-than-expected plants with reduced root systems in the garden: but the bad news is that there is not a lot that can be done to eradicate these unpleasant creatures. Chemical pesticides which kill flatworms also kill earthworms, defeating the purpose of the exercise; the flatworm has few natural enemies in countries where it is an alien species; and, while immersing infested containers in water at 30°C for 20 minutes kills adult flatworms, this is not possible in the garden. Chopping them up or trying to increase the earthworm population through the provision of soil organic matter are about the only actions the gardener can take. To find out more, go to the CABI website, the source of many of my facts.