Both snails and slugs have a definite mouth, which is equipped with a horny file, or radula, with which they rasp away the substance to be eaten. Slug damage to crops varies considerably with the season and year. Slugs can cause serious farm, home garden, and greenhouse losses. They damage plants by eating the leaves and tender shoots, attacking almost all field and garden crops, including grains, clovers, corn, young vegetables, ornamentals, and small fruits. They are especially attracted to ripe strawberries and tomatoes.
Some slugs are also injurious in mushroom houses.
Slugs leave a slime trail of mucus on the surfaces on which they crawl, and, on drying, silvery marks result which are objectionable, especially on floral or ornamental plants. Very humid environments favor the development of slugs and snails. Snails and slugs are mainly nocturnal, but they come out of their hiding places and feed in the evening or on dark days. Snails are less particular in this respect than slugs, since they can seal the opening of the shell with a mucous sheet, the operculum, which soon hardens to a leathery texture. Under adverse conditions, the snails become dormant for up to 4 years.