Predators
Frogs, toads, snakes, hedgehogs, salamanders, eastern box turtles, rats, caecilians and also some birds and beetles are slug predators. Slugs can be a vector of transmission of parasitic nematodes that cause lungworm in various mammals, so are usually avoided by hedgehogs and other mammals when other food is available.
Slugs, when attacked, can contract their body, making themselves harder and more compact, and combined with the slippery mucus is more difficult for many animals to grasp. The unpleasant taste of the mucus is also a deterrent.
Some slugs can self-amputate (autotomy) a portion of their tail to help the slug escape from a predator.
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