I came across this very distinctive worm in my garden this afternoon. I didn’t know what it was, but had a horrible feeling that it wasn’t good. I was right! It’s one of the ten or so foreign predatory flatworms that are spreading across the country, brought in accidentally in plant compost. They feed on earthworms and other soil invertebrates, some species becoming invasive and having a hugely detrimental effect on soil health. Parts of Scotland and Ireland have been particularly badly affected.

I think this one is Caenoplana variegata, first recorded in the UK in 2008 but native to Australia. There were two of them under a plastic sheet among lots of earthworms and other invertebrates. The earthworms wriggled in the sun and headed off along the path within seconds. In contrast,  the flatworms took longer to extend and make a move but when they got going they put on quite a turn of speed. The leaf is about 3 cm long.

                                                           

This species has a distinctive yellow stripe but they come in various forms. We have four native species of flatworm but they are much smaller and are found in freshwater environments, so any found in the soil are usually non-native.

We are very aware of Himalayan balsam and Japanese knot-weed, but less so of the potentially catastrophic damage these accidentally introduced animals are doing at the bottom of the food chain. Shouldn’t we be more careful about introduced garden plants? It certainly make me feel uneasy about all the exotic plants I’ve bought from garden centres over the years.

It is recommended that you don’t share plants in soil from an affected garden. There is unfortunately very little to be done to control them otherwise.

If you find a flatworm in your garden, you can help chart their spread by completing the Buglife Flatworm Survey.

Julian Birkhead