Experts have confirmed non-native Obama flatworms have been found in two locations across Alderney.
Obama flatworms (Obama nungara) were first identified in Guernsey in 2008, but had not been recorded on Alderney until now.
The dark flatworms with pale undersides are native to southern Brazil and Argentina.
Ecologist Matt Lewis is concerned about the potential impact of their diet.
"We’re particularly concerned about the impact on our earthworm population.
"Earthworms do loads of brilliant things within garden systems and natural systems, aerating the soil, increasing fertility.
"So anything that’s kind of affecting the earthworm population, especially something that shouldn’t be here, is something we might be concerned about.
"Studies in France, where they have looked at the guts from these (Obama) flatworms, they have found earthworm species in every flatworm they have looked at."
The Alderney Wildlife Trust is asking islanders to look out for the Obama flatworms, report any sightings to the Alderney Biodiversity Centre, and dispose of any in hot or salted water.
Moving plants from gardens where Obama flatworms have been found is also discouraged to slow the spread.
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