Creature Feature: Land Mollusks

Have you ever walked outside barefoot on a damp summer’s evening and felt slime in between your toes—only to realize with disgust that you stepped on a slug? 

Or, have you waited for a strawberry to ripen on the vine and as you lift up that perfect fruit you find a gaping hole in its underside with a slime trail leading to it? I have done both.

Mollusks are soft-bodied animals that can live only in water or very moist conditions. Oysters, clams and nudibranchs are types of mollusks that live underwater. Snails and slugs have escaped from living in water to living on land. They can literally drink water through their skin but they also lose water the same way. During dry spells, they hide under rocks or logs. 

In the winter, they stay deep in the ground to avoid freezing. In the spring, they emerge and start feeding on vegetable material. That includes newly-emerging garden sprouts, algae on the side of a house and berries.

They also begin their reproduction cycle in spring. One of the most interesting things about these mollusks is that they are hermaphroditic. They are both male and female at the same time but need another animal to fertilize the eggs they carry. Two animals will exchange sperm and both will later lay up to 300 eggs in clusters of 30 in damp soil. In about a month the eggs will hatch. The tiny young animals spread out in all directions. Their life span can be as long as four years.

To prevent snails and slugs from bothering your garden, you can use several non-toxic tricks. The mollusks cannot live if their skin dries so remove as many daytime hiding places as you can find: rocks, wood, and dense ground cover. Diatomaceous earth crushed into a fine powder will dry them so much that they avoid it. Spread the powder around the base of plants. Unfortunately, it needs to be reapplied if it gets wet.

Slug hunting at night with barbecue tongs can also reduce the damage.

Interestingly, the mollusks cannot cross a ribbon of copper. It is speculated they get a small unpleasant electric shock when they touch the copper if it isn’t enameled. Some people have also found success in laying open beer cans (with some leftover beer inside) on their side in the garden. The yeast attracts the snails and slugs and they die in the remaining alcohol.

Slugs and snails do have some natural enemies. Toads, snakes and birds will eat them but there are usually not enough predators around human dwellings to keep their populations in balance.