Within the Phylum Mollusca, the scientific Class Gastropoda includes snails and slugs.  Slugs have rasping mouthparts and most slugs have two pairs of tentacles.  The eyes of the slug are located on the longer pair.  A slug's body resembles a snail's, but the shell of a slug is small and underneath the animal's skin, while snails have a large external shell.  The slug breathes through a hole called a pneumostome that opens into a cavity in its mantle.  The mantle is a flap of skin just behind the slug's head. Slug skin is sensitive to water loss so slugs use mucus to remain moist.  

Slugs can be easily distinguished from the other critters on this website: slugs belong to the Phylum Mollusca (the mollusks, which also includes squid, octopi, snails, clams, and oysters).  The other animals on this website belong to the Phylum Arthropoda (insects, spiders, mites, scorpions, etc.).  Like arthropods, mollusks have an exoskeleton, but arthropods have jointed, articulated legs, while mollusks do not.  

Some slugs have an annual life cycle, others a biennial, and still others a plurenniel life cycle.  They usually lay their eggs in holes or underneath debris.  The number of eggs per batch and the number of batches vary between individuals.  For example, the gray field slug can lay up to 500 eggs per year and the black field slug lays from ten to thirty eggs per batch in captivity.  Young slugs are small versions of adult slugs.  The life span of a slug is one to six years, depending on the species.

Slugs prefer cool, dark, moist habitats.  In woodland areas, they can be found under bark, logs, and other woody debris.  In urban and residential areas, they are usually found under objects such as pots and garden ornaments or in garden mulch.  Slugs are most active just after sunset and in the early morning hours before dawn.  If the temperature becomes too hot or dry, slugs will retreat deep into the soil and return to the surface when conditions improve.

Slugs have very diverse dietary habits.  Invasive slugs can be very destructive, feeding on flowering and leafy garden plants, as well as crops such as wheat and corn.  These animals usually feed at ground level or just below the surface of the soil.  Native slugs feed on fungi, lichen, carrion, and plant materials in wooded areas.  They are very important for nutrient cycling.

There are many predators of slugs including birds, non-avian reptiles, and amphibians.  Probably the most common predators of slugs are insects, particularly ground beetles.

Pictured below are some of the most common slugs found in Kentucky. For a complete list, along with a detailed scientifc key, visit the University of Kentucky College of Agriculture publication:
SR-103 - A Field Guide to the Slugs of Kentucky (PDF)

BLACK FIELD SLUG
FAMILY: Arionidae | GENUS & SPECIES: Arion hortensis & others
Like most slugs in Kentucky, the Black Field Slug is native to Europe.  It can be recognized by its yellow "sole" and the yellow mucus it produces.  The black field slug can live up to one year and reach a length of 3 cm.  It is most common in areas associated with people, such as lawns and gardens. The species Arion hortensis is actually a species complex composed of three individual species. These species are Arion hortensis s.s., Arion distinctus, and Arion owenii. Dissection or molecular techniques are necessary to tell the members of this species complex apart.

HEDGEHOG SLUG
FAMILY: Arionidae | GENUS and SPECIES: Arion intermedius
The Hedgehog Slug is also native to Europe. It can live up to one year and is the smallest slug in Kentucky, only growing up to 2 cm. This slug is yellowish-gray in color and is named for the raised tubercles on its back which look like spikes when the animal is contracted. The hedgehog slug's head and tentacles are a darker gray than the rest of its body. This slug can be found in gardens, but is more likely to be located in grasslands or agricultural fields.

To find slugs, look underneath logs or in the drainage holes of pots.  If it is a humid night, you will probably see them climbing your home or crossing your sidewalk. You can also set traps for them by placing carrot slices under a potting saucer and leaving it overnight.  However, be sure to check it early in the morning, since they do not stick around for long after the sun has come up. 

Slugs are typically easy to photograph as they do not move too quickly.  Since they are often found in dark places, though, you may need a flash or a fast film speed to get a good picture.  

Besides keeping the slug moist, slug mucus also has several other functions. It aides in movement by protecting the slug from damage as it travels and it plays a role in courtship and mating. Slugs also use their mucus in defense. Most species of slugs secrete mucus to make it difficult for a predator to hold onto them or to make them taste bad. 

Slugs are hermaphroditic, meaning each slug contains both male and female sexual organs. When environmental conditions are harsh, a slug can fertilize its own eggs and therefore does not need to mate to produce young. 

Do you know any myths, legends, or folklore about slugs? If you do, please let us know!