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Earthwormsuseful soil improvers, but a problem in the wrong habitat.Worms left in the wild after fishing trips are harming rare native woodland plants around the Great Lakes.
Writing about earthworms in 1881 Charles Darwin said: ‘It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organized creatures’. Earthworms are well known to most Americans as gardeners’ friends and useful fishing bait, but they are rarely though of as ‘invasive species’. The European Earthworm (Lumbricus rubellus) arrived in America with the first settlers from the British Isles. There were very few native species to compete with and it spread happily through agricultural areas where it helped improve soil fertility. Unfortunately it also managed to spread into some of the broadleaved forests which had never known earthworms. Here the delicate ecology relies on the fact that fallen leaves are not consumed by helpful earthworms. The most famous casualty is the rare Goblin Fern (Botrychium mormo), a moonwort which requires a forest litter unmodified by earthworms. Fishermen probably released earthworms around the Great Lakes at the end of their fishing trips. It might seem ‘poetic justice’ that the European earthworm is now under threat in its native Europe from yet another introduced species. In this case the New Zealand Flatworm (Arthurdendyus triangulatus) was brought in with exotic plants in 1960. It is now found in many garden centres and has ‘escaped’ into the wild. The problem is that it eats earthworms and, like many introduced species, has no natural enemies in its new home. This is a disaster that is still unfolding. The European Earthworm is a ‘generalist’ – it is comfortable in most types of soil. The Brandling Worm (Eisenia foetida), on the other hand, is very much a ‘specialist’ – happy only in decomposing vegetable material. This makes it one of the favourites of keen gardeners who keep a wormery. The worms are kept in a small container and are fed with waste vegetable materials. They convert this waste material into a useful compost for the garden. When this species escapes from the wormery it is not likely to go far – just as far as the next compost heap! Both the European Earthworm and the New Zealand Flatworm are examples of species that have been accidentally introduced into new habitats by gardeners. As with all introduced species it is extremely difficult to predict the outcome. In the case of the European Earthworm in America the problems have taken centuries to show up and might not be disastrous – but in the case of the New Zealand Flatworm the effects have been immediate, and if the British earthworms continue to be gobbled up there could be serious consequences for agriculture. Be careful with worms at the end of a fishing trip. Take them back home with you and put them in your wormery! Like this? – see what else I have written.
The copyright of the article Earthworms in Other Invertebrates is owned by John Blatchford. Permission to republish Earthworms in print or online must be granted by the author in writing.
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