We recently received a photograph of a black worm-like organism on asphalt. The reader who sent the photo asked the classic question, “What is this?” The specimen is smooth, black, and has two tiny appendanges coming off its head. We are confident that this creature is a slug!
Slugs aren’t worms, they are actually terrestrial mollusks. Most mollusks have shells, but slugs don’t. Instead they have tough skin and secrete a mucus film for protection. The two appendages coming off the slug’s head aren’t antennae, they are optic tentacles. Slugs can move their two optical tentacles independently of each other to look around at their surroundings and to use for smelling. Slugs have two smaller sensory tentacles below their optical tentacles that they use for feeling and tasting. Most slugs are generalists, which means they feed on a wide range of organic materials, but some slugs have predatory eating habits and consume other slugs, snails, and earthworms.
There are about 5,000 known species of slugs around the world. We aren’t sure which species our reader is dealing with, but based on its appearance we think think it might be a black slug or a black velvet leatherleaf slug. Black slugs, also known as black arions or European black slugs, are found in northern Europe, Canada, the Pacific Northwest, and Australia. Black slugs are nocturnal and prefer cloudy days to sun exposure. Like black slugs, black velvet leatherleaf slugs also like cloudy cover and high humidity. Black velvet leatherleaf slugs are originally native to South America, but they are now found in the southeastern United States, where they are considered an invasive species. This slug might also be a species besides black slug or black velvet leatherleaf slug.
In conclusion, we are confident that the black worm-like organism our reader discovered is a slug. We think it could potentially be a black slug or a black velvet leatherleaf slug!