|Urban Knowledge Master|
Slugs and Snails
Veronicella cubensis (Pfeiffer)
Veronicella leydigi (Simroth)
Achatina fulica (Bowdich)
Bradybaena similaris (Ferussac)
Helix aspersa (Muller)
Julian R. Yates III
Extension Urban Entomologist
College of Tropical Agriculture and Human Resources
University of Hawaii at Manoa
Of the slugs most commonly asked about, Vaginulus plebeia Fischer, Veronicella cubensis (Pfeiffer), and the black slug,
Veronicella leydigi (Simroth) top the list. Pestiferous snails that are often encountered in residential flower beds, vegetable gardens, and commercial farms include the Giant African snail, Achatina fulica Bowdich, Small Garden snail, Bradybaena similaris (Ferussac), and the brown garden snail, Helix aspersa Muller.
Slugs and snails thrive in humid and wet areas and are damaging pests of fruit trees and vegetables, and are annoying when they crawl over walks, porches, walls of homes, and invade homes through doorways. Their mere presence and trail of thick slime, which can persist for several days, are extremely unsightly. When they are accidentally stepped on or crushed beneath a car tire, the result is a repulsive mess and odor.
Nine varieties of slugs and about two dozen of land and freshwater snails are reported on the islands of Hawaii.
They feed on decaying vegetable matter, fungi and molds, earthworms, dead or slow-moving insects, plant stems and trunks, leaves, flowers, and roots by scraping off the tissue or eating holes in the plant parts. The tawny garden slug, Limax flavus Linnaeus, has been observed to feed completely around the trunks of mature banana trees, near ground level, which results in their toppling. In other banana plants, it has bored through the trunk and hollowed out the corm, making a living space for several L. flavus adults. The African snail is a carrier of the rat lungworm, which causes eosinophilic meningitis.
Structurally, snails differ from slugs by possessing a spiral shell. The shell consists of calcium, which the snail deposits to increase the shell size as it grows. The shell of the giant African snail can attain a length of 15 cm. In other aspects, the two are quite similar in structure and biology. Both have eyes mounted at the tips of stalks on the head, are legless, and move by means of a "foot". Glands in the foot secrete mucous to facilitate movement. Both animals are hermaphroditic (i.e., individuals possess both male and female sex organs; however, mating is required) and both animals may lay eggs.
The oval, translucent eggs, 10 to more than 200, depending on the species, are laid most often in moist soil at a depth of approximately 2.5 cm. These eggs are about 3 mm in diameter. Depending on the weather, incubation (egg laying to hatching) will vary, but the average is 14-30 days.
No information available.
The young are very small when they hatch, and they will remain near the place of hatching, returning there each morning, for several months. They reach sexual maturity in about three to five months, and may take as long as two years to become full-grown.
Slugs and snails are nocturnal. During the day they seek shelter beneath pieces of wood, plants, pottery, rocks, decaying logs, damp refuse, mulch, and fallen leaves, to hide from the sun. They are extremely susceptible to drying out. The snail has an edge over the slug, however. Under unsuitable conditions, the slug will take refuge in its shell and seal the opening with slime that will harden into a thick, leathery material called the operculum. Some snails can remain in this dormant condition for as long as four years. When suitable conditions recur, they chew through the operculum and resume their normal activity.
Sanitation is the safest, cheapest, and surest method of controlling these slimy pests. It is done by eliminating the hiding and breeding places and correcting moist conditions in basements and crawl spaces. In addition, pieces of boards can be placed on the ground in areas vulnerable to attack to trap these pests. Another trap can be fashioned by pouring beer into a shallow pan. Beer is highly attractive to slugs and snails, and they will crawl into the pan and drown.
The rosy predator snail, Euglandina rosea (Ferussac), the cannibal snail, Gonaxis kibweziensis (Smith) and the carnivorous snail, Gonaxis quadrilateralis Preston, Figure 5, were purposely introduced into Hawaii to combat the Giant African snail.
Natural predators of slugs and snails include toads, some predacious beetles and their larvae, birds, ducks, and chickens.
Commercially prepared slug and snail baits containing the active ingredients metaldehyde or methiocarm (Mesurol) may be used to further control these pests.
Ebeling, W. 1978. Urban entomology. Division of Agricultural Sciences, University of California, Berkeley.
Heu, R. 1988. Hawaii Department of Agriculture. Personal communication
Mallis, A. 1982. Handbook of pest control. Cleveland: Franzik & Foster Co.
Nakahara, L. 1982. Survey of two slugs new to Hawaii. Hawaii Department of Agriculture. Unpublished computer listing.