P&PDL Picture of the Week for
May 23, 2005

Snails - Mollusks out of water

Tim Gibb, Insect Diagnostician, Department of Entomology, Purdue University

Snails are not insects but rather gastropods and if the Greeks have their definitions right, gastropod means ‘stomach-foot’. These animals are more closely related to clams and mussels than they are insects.  They are easily identified because of the characteristic hard shell on their back and their single, broad, muscular foot upon which they move about. Two pairs of ‘tentacles’ protrude from the front end of the snail, the larger pair tipped with eyes are for sight and the smaller, anterior pair for sensing odors. 

Snails may occur on a large number of plants but generally require conditions that are moist and abounding in decaying organic matter. 

The brown garden snail, see photo, is an introduced pest and is common throughout the nation.  It can live multiple years.  It can survive the winter by sealing itself off inside its shell by using a thick membrane called an epiphragm (in case you were looking for an unusual babies name).  It is active during the spring and summer and lays eggs in the soil during the fall time. 

Snails have a unique mouthpart that is used to scrape and rasp the vegetation on which it feeds.  This can result in either holes or simply a discolored area of the leaf or stem where the snail has eaten away the epidermal leaf tissue.  In either case the plant can become unsightly very quickly.

Many different cultural control methods have been tried and many have been touted as being effective.  Common among these is the recommendation of using salt.  When applied directly it will immediately desiccate the snail and instill a great sense of satisfaction within the applicator.  The snail quickly retreats inside its shell and squirms spastically before shrinking up to near nothing.  When used on the ground around a plant, the salt will help keep the snails at bay, however, avoid using enough salt to poison the plant or change the characteristics of the soil. 

Beer has been used in shallow trays or dishes as bait for snails.  The fermenting liquid (wine works equally well) attracts the snails, whereupon they crawl right into the saucer and apparently drown. Drowning in beer may not be the most dignified death, but at least they die with smiles on their little faces.

Wood ashes, certain soaps and copper foil are also reported as effective barriers to keep snails out.  Insecticides usually have little effect on snails because snails are so dissimilar to insects.  Baits that include ‘iron phosphate’ or ‘Metaldehyde’ as the active ingredient are labeled for snail control and can be purchased at most garden centers.  Placing these materials during the late afternoon or evening (snails feed at night) and under the canopy of the plant (sunlight breaks down the product), preserves their effectiveness. 

Hand picking snails is also an effective means of control in localized areas.  Snails congregate during the daytime under boards or wet newspapers lying on the ground.  This behavior can be taken advantage of by congregating and then physically destroying the snails.

Long-term controls depend upon reducing their preferred habitat in some way.  Reducing the amount of moisture and/or organic matter by adjusting irrigation and or mulching activities can be some of the most effective ways to control these little ‘one-footed, shell toting stomachs’.

Click on image to enlarge

Brown garden snail (Helix aspersa)

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service