31 Aug 2016

Giant slugs are eating young hatchlings in their nests, claim two Polish scientists.

The pair, colleagues at universities in Wroclaw and Zielona Góra, were engaged in a study of common whitethroat birds when they came across a slug of the Arion genus in a nest of newly hatched chicks. On returning the next day, the scientists found a nest full of dead chicks, with injuries suggestive of the slug’s involvement.

“We couldn’t believe that the slug had killed the nestlings,” Kararzyna Turzańska told New Scientist magazine. “We talked to many experienced ornithologists, but none of them had observed slug predatory behavior towards birds before.”

However, Turzańska and her colleague Justyna Chachulska discovered that their observation was not the first time such behavior had been observed. Mainly in Europe, the reports detailed suspected slug attacks on a number of ground-nesting species.

“The actual moment of slugs predating on nestlings isn’t easy to observe,” says Turzańska. “You are more likely to come across the traces of the ‘tragedy’: hatchlings with injuries, covered in slime, and slug droppings found nearby.”

The species concerned are some of Europe’s largest slugs – the roundbacks, including the so-called ‘Spanish’ slug, Arion vulgaris. This is regarded as an invasive species and is well-known for its predation on earthworms and even other slugs.

New Scientist; Journal of Avian Biology, DOI: 10.1111/jav.01189