Slug Hunting

Community Contributed by Glenn I. Teves, County Extension Agent

For many, a slug is just a slug, but there are over nine varieties of slugs in Hawaii, including brown ones, black ones, and striped-back ones. To control them, you treat them all the same way. Get rid of them before they get your food or your beautiful plants.
Slugs thrive in humid and wet areas, and are damaging pests of fruit trees, ornamentals, and vegetables. In dry areas, they’ll start moving on the first rain, and do most of their work at night. They can be very damaging in a garden with tender seedlings by chopping them off at the stem. Slugs are mobile and can cover 20 feet or more in a night.

Slugs feed on decaying matter, fungus, molds, earthworms, dead and slow-moving insects, plant stems, trunks, leaves, flowers, and roots. Their feeding action is by scraping or rasping, and can skeletonize a leaf, leaving the thick parts of the leaf remaining. The tawny garden slug can feed completely around the trunk of a banana plant near ground level, and can topple it. It can even bore a hole in the trunk, hollowing out the corm, creating a new venue for a slug fest.

Slugs have eyes mounted on the tips of stalks on their head that look like antennas, and move by a ‘foot’ whose glands secrete mucous to help them glide along, especially on wet ground. Slugs are hermaphrodites; they possess both male and female sex organs. However, mating is required, and when mating, both animals can lay eggs. This means every mature slug can lay eggs which is why they multiply so fast. The eggs are oval and translucent, and slugs lay anywhere from 10 to more than 200 eggs, depending on the species. Eggs are about one-tenth of an inch in diameter and are laid in moist soil about 1 inch deep. Eggs can hatch in 14 to 30 days.

The young slugs are very small when they hatch, and will remain near the place of hatching, returning here each morning for several months. They’re of breeding age in three to five months, but some may take as long as two years to become fully grown. They seek shelter from the sun during the day under just about anything, even concrete slabs, since they’re susceptible to drying out.

There are many ways to control slugs. Hand picking is very effective. On the first indication they’re moving around, especially after a rain or a humid night, you can spend an entertaining evening either picking them up or smashing them. Copper is very toxic to slugs, but must be kept clean and untarnished to be effective. Just by sliding over copper, they can die. Placing pennies in high population areas can control slugs, but only pennies dated before 1982 will work since they’re 95 percent copper. Some made during 1983 and all in 1984 and beyond won’t kill them since they’re 97.5 percent zinc with a thin copper coating. Since a penny isn’t worth a penny anymore, this may be a worthwhile investment. Two very effective stomach and contact poisons found in slug bait formulations include metaldehyde or methiocarm, also sold as mesurol. A natural alternative is iron phosphate, used in slug bait formulations such as Sluggo. There are home remedies such as beer and 1-2 percent caffeine from coffee and coffee grounds. They drown in the beer and caffeine is toxic to them. Other natural controls include toads, predacious beetles, birds, ducks and chickens. Putting a board on the ground to attract them is another technique. They’ll congregate under the board and you can catch a whole gang of them. Happy slug hunting!