Slugs 'transporting worms in guts'
Slugs may not be the most welcome visitors to the garden, but they provide a vital public transport service for small worms, a study shows.
Tiny nematode worms use the slimy molluscs as taxis as they travel around in search of decomposing fruit and rotten plant material on which to feed.
Their "carriages" consist of the slugs' guts. After invading the creatures' intestines, the proliferating nematodes make themselves comfortable before journeying to a far-off new location and being excreted.
Scientists believe the worms, which are only a millimetre long, may also hitch rides in woodlice and centipedes
Changing temperature and food availability make it necessary for the worms to move around a lot, but until now little was known about how they managed to travel long distances.
Lead researcher Dr Hinrich Schulenburg, from Christian-Albrechts University in Germany, said: "Even though nematode worms are one of the most intensively studied organisms in almost all biological disciplines, we still have very little understanding of their natural ecology
"Our study reveals a previously unknown nematode lifestyle within the guts of slugs. The worms appear to have evolved to persist in the harsh environment of slug intestines, similar to a symbiont or even a parasite."
Searching gardens and compost heaps, the scientists collected more than 600 slugs and over 400 other invertebrates including flies, centipedes, spiders, beetles and locusts.
Analysis showed that nematode worms were commonly found in slugs, woodlice and centipedes, having probably been eaten unintentionally.
Further experiments confirmed that the worms survived and reproduced in the guts of slugs before being excreted alive in faeces.
In laboratory tests, the researchers watched what happened when 79 slugs were exposed to more than a million fluorescently-tagged worms.
They found that the worms survived the entire passage through the slug digestive system.
But they remained inside the slugs for no more than a day - suggesting that long journeys are made by taking a number of different taxi rides.
Carrying the worms appeared to cause the slugs no harm, said the scientists, writing in the open access journal BMC Ecology.