Follow the slime trail
The links in this article from 2008 were updated in June, 2011, and March, 2013.
Garden snails, Zachrysia provisoria, can cause devastating plant damage. At night time they are often found on the foliage feeding. They can chew irregular holes in leaves, or create a series of perfect circular holes just by grazing on an unopened leaf. Also snails feed on fruit and nonwoody plant bark.
Not all feeding damage can be blamed on snails.
Snail Management relies on a combination of methods. Remove or reduce habitats that they are likely to hide under such as boards, bags, and brush debris. Snails may be a sign of an over-watered landscape. Look for slime trails at night. Handpicking can be effective if done on a regular basis. Water the infested area in the late afternoon and search out the snails after dark. Discard into a plastic bag or a bucket with salty water. Traps can be used to attract snails. For example, slightly elevating a board overnight above the ground near damaged plants makes an attractive shelter. They can then be collected in the morning. Attractive substances such as beer or decaying fruit will draw them out. Take a shallow saucer and sink it into the ground so that the edge is level with the ground. Place some beer and a few slices of banana in the saucer. The snails crawl in and cannot get out. http://ipm.ifas.ufl.edu/pdf/Garden%20Snails.pub%20(Read-Only).pdfIf the use of a pesticide is necessary for snail control then metaldeyde, metaldehyde/carbaryl or iron sulfate (Sluggo or Escar-go) baits are recommended chemicals for controlling slugs and snails. Baits can be hazardous and should not be used where children and pets cannot be kept away from them. Iron Phosphate bait has the advantage of being safe for use around domestic animals and wildlife. Most garden centers sell a slug and snail bait. The bait should be placed on the soil surface in the vicinity of the plants and the treated area can be covered with several sheets of newspaper soaked with water. Apply the bait in the afternoon or at night. If possible, do not use the bait just before a rain, as its effectiveness will be reduced.
Slugs and snails may feed intermittently rather than every day, therefore, distributing the bait at 7 to 10 day intervals until control is achieved is recommended. Read and follow all pesticide label instructions.
Department of Plant Industry
Dr Bob’s gardening Tips, Snails & Slugs