What is a Slug?

Most of our native Michigan slugs feed on fungi, lichen, carrion, and plant materials in wooded areas and are very important for nutrient cycling. The non-native invasive slugs, however, can be very destructive, feeding on flowering and leafy garden plants, as well as crops such as wheat and corn.

Slugs belong to the Phylum Mollusca (the mollusks, which also includes squid, octopi, snails, clams, and oysters). Slug parts up close are very interesting (see diagram). Their skin is sensitive to water loss so they prefer cool, dark, moist habitats. If you’re not into looking under rocks and leaves, the best time to hunt slugs is just after sunset and in the early morning hours before dawn.

Slugs produce two types of mucus: one which is thin and watery, and another which is thick and sticky. The thin mucus is spread out from the center of the foot to the edges to help prevent the slug from slipping down vertical surfaces. The "slime trail" that a slug leaves behind helps other slugs find mates. The thick mucus spreads out to coat the whole body and provides some protection against predators by making it hard to handle. There are many predators of slugs including birds, reptiles, amphibians and ground beetles.

The Gray Field Slug Deroceras reticulatum is not native to North America, but has been in Michigan as long as the earliest European settlers. Their skin color can vary greatly and they can grow to be 5cm. Take a peek under your hosta plant leaf tonight and get up close to a slug. Fascinating creatures!