Slug and Snail Biology



HABITAT: Because of their soft, gooey bodies, slugs need a moist environment. Dry air desiccates them. Most slugs, in fact, live underground. The slugs that are feeding in your garden are most likely only a small fraction of the population that actually lives there.

Cool weather, rain and fog bring out the best in slugs. Without an outer shell to protect them, slugs may dry out in warm, dry weather.

 During dry spells, slugs seek a moist, dark environment. They retreat into the soil, under mulch, or cling to the bottom of boards, rocks or old flower pots. If the dry spell persists, they can encase themselves in papery cocoon-like structures and attach to a porch or garage wall or a tree and wait it out, a tactic called “aestivation.”

FOOD: Slugs and snails grind up their food, be it tender leaves, seedlings, soft fruits, fungus, or decaying matter with rasp-like teeth. You can lessen damage and ensuing cursing and frustration by planting species that are not slug favorites like these plants.

PREDATION:  Many animals can see beyond the slime and general unattractiveness of the slug enough to feed on them regularly. Raccoons, hedgehogs, toads, turtles, skunks, snakes, ducks and chickens will just as soon snap up a slug as look at it.

When attacked, a slug’s first defense is to run away. That never works. Next, it will contract its body, becoming a smaller, more compact target. The mucus that covers the slug tastes nasty and is slippery, sometimes allowing the slug to be spit out and to make an escape.

A few species can self-amputate a portion of the tail when caught, leaving the predator with a “What the heck?” expression while the slug creeps away. The tail is later grown back.


Slugs are hermaphrodites; they have both male and female genitalia hidden under their mantels. These sexual organs come out only when an especially attractive possible mate appears. What constitutes an attractive slug? One that will let another slug mate with it. Not too picky, but that expands the slug dating and mating world extensively.

Since slugs are such slow movers, they cannot afford to wait until the third date to go for it. One may follow a slime trail to another slug, introduce itself, and get down to business.

The mating dance begins as the slugs encircle each other and exude a heavy layer of slime. When both parties are ready the genitals are extended from under the mantel.

Slugs practice (and have probably perfected) “apophallation,” the entwining of corkscrew-shaped penises for the exchange of sperm. Sexy as it sounds, the corkscrew method is more easily done than undone. Mating often ends with one or both slugs chewing off the other’s penis.

The slug-sans-penis is still able to mate using its female sex organs, but must develop a more feminine outlook on the whole game.