Slug, a tough skinned mollusk, is usually harmless to other animals, until it started to attack poor baby birds in Poland.
Now being dubbed as the monster slugs, New Scientists reports they have been spotted devouring baby birds on their nests while their mother bird is out for a hunt.
"The actual moment of slugs predating on nestlings isn't easy to observe," says Katarzyna TurzaÅ„ska at the University of Wroclaw in Poland told the website. "You are more likely to come across the traces of the ‘tragedy': dead or alive nestlings with heavy injuries, covered in slime - and often slugs' droppings found nearby."
Injuries caused by the slugs are usually grave. It can span from bleeding wounds, holes in the stomach with viscera exposed, vast skin lesions on wings, back,neck or head, partially eaten muscles or bills, even loss of eyes.
This behavior, as explained by the paper published in the Journal of Avian Biology, may have an effect on the breeding success of some passerines in the near future.
The researchers who reported on the predation identified the creatures as Arionid slugs. According to the records of University of Florida, the Arionid slugs are garden slugs that can grow up to 25 to 30 mm. They usually feed on narcissus, grasses, lilies, (leaves, brood bulbs, flowers), and iris in greenhouses.
Predation of slugs on birds is rarely reported and is very uncommon. Only few papers have reported cases about it.
The first report was made in 1920 when they were seen harming Skylark Alauda arvensis. But what surprised the researchers more is that accounts from those who have previously seen the predation tells that slugs usually attack the nests close to the ground.
In Turzańska's and colleague Justyna Chachulska's research, however, it showed that the slugs went far to attacking those nests that are already on tree top. The researchers hypothesize that since the sense of smell of slugs is strong, they might have been using it to forage for the poor birds.
"When a slug finds itself inside a nest -- probably accidentally, or maybe by actively searching for this type of food -- it just starts foraging on the living nestlings using its radula, or tongue covered in tiny teeth," says Turzańska. "The nestlings are unable to defend themselves and are eaten alive."
The predation is especially tragic as the research has also not seen the mother bird defend their off springs in events like these.