What Are Land Snails and Slugs?
Land snails and slugs, as well as aquatic snails, are types of invertebrate animals known as mollusks. Within the mollusk group, these organisms are members of the Class Gastropoda, a classification category meaning “stomach-foot.” They move on their belly on a large, muscular foot. For those gastropods with a shell, their organs are inside the shell.
What Do They Look Like?
Land snails and slugs have tentacles on their head. The tentacles detect chemicals. Most land snails and slugs in Illinois have an eye at the tip of each upper tentacle. Snails have an external shell. Slugs may have a very reduced shell under their mantle or no shell. A snail’s shell develops in the egg along with the rest of its body and continues to grow until the snail reaches maturity. A snail cannot leave its shell. Each species of snail has its own type of shell. The features of a shell can help to identify the type of snail that produced it. Some snails have denticles, or “teeth,” around the shell opening to prevent insect predators from entering and eating the snail.
How Big Are They?
There are about 124 kinds of land snails and slugs in Illinois. The smallest snail is about 0.05 inch long, and the largest one is about 1.80 inches long. Slugs can be two to three inches in length, depending on the species.
Where Do They Live?
Snails need to seek sheltered places to live, eat and rest. They prefer to live in moist areas and are commonly found under logs, loose bark or coarse woody debris, and in leaf litter on the forest floor. Snail populations tend to be greatest in areas that have high amounts of calcium in the soil. Calcium is needed to produce the shell and to regulate body functions.
How Do They Reproduce?
Most land snails are hermaphrodites, possessing both male and female reproductive organs. When snails mate, fertilization often occurs in both individuals, and both lay from one to at least 20 eggs in a clutch. The number of eggs per clutch varies by species. Generally, the larger the snail, the more eggs it will lay. Snails lay their eggs in spring and fall. Eggs are deposited in a cool, damp place, often just under the soil’s surface. The adult snail provides no care for the eggs. Hatching takes place in about seven to 10 days. The young snails emerge and begin to search for food immediately.
What Do They Eat?
Most Illinois land snails eat decaying vegetation, such as leaves and plants. Some snails feed on other snails or dead animals. In Illinois, the gray-foot lancetooth snail (Haplotrema concavum) eats other land snails. It has a thin, elongated “neck” that it inserts into the shell of other snails. Its special barbed teeth attack the flesh of the prey snail.
Does Anything Eat Them?
Snails are a food source for many animals. Some insects eat land snails. Firefly larvae feed almost exclusively on snails. Many birds eat snails. The wild turkey (Meleagris gallopavo) is an example of a bird that regularly eats snails. Female birds that normally eat snails may increase their snail consumption when they are preparing to lay eggs. The calcium in snail shells helps young birds develop before they hatch and aids the female bird in producing the shell. Toads eat snails and slugs as do squirrels, mice, millipedes, centipedes and other small animals.
What Else Should I Know About Them?
The external skin of snails and slugs produces mucus to prevent the snail or slug from drying out and to help it move. During very hot, dry weather and during very cold periods, snails and slugs may become inactive. When that happens, a thick mucus membrane is produced over the opening of the shell to keep moisture inside.
Land snails and slugs move very slowly. One snail was recorded to be moving at 0.0023 mph. At this speed, it will take a snail about five minutes to move one foot!