Although there are over 20,000 species of snails, just two are responsible for the bulk of the damage to garden plants.
Brown Garden Snails (Cornu aspersum)
The most common garden snail around the world is Cornu aspersum, the brown garden snail. This snail’s shell is about 25 mm (1 inch) wide with four or five whorls in a distinctive brown and gray pattern. Brown garden snails originated in ancient Rome, and were carried throughout the Roman Empire as a food source. Huguenot settlers carried it to South America to provide their escargot. Italian settlers took it to California, Australia, and New Zealand. The snail thrives in cold climates as far north as Quebec in Canada, and in desert climates as arid as Utah and Arizona in the USA. The states of Arizona, California, Louisiana, Mississippi, Oregon, South Carolina, Texas and Washington in the USA quarantine shipments of plants from other states to reduce the spread of the snail.
One of the reasons brown garden snails are so successful is their “belly dance.” All snails travel on a pool of mucus they secrete. Brown garden snails arch their bellies so that only about 1/3 of the bottom of the snail ever touches the ground. This allows the snail to conserve mucus and the water required to make it. Traveling just one meter (3 feet) can require 1% of most snails’ body fluids. Brown garden snails can travel three times as far on the same amount of stored water. Cornu aspersum is among the speediest of all land snails, having been clocked at a peak speed of 24 cm (10 inches) a minute, moving as much as 20 times faster than other kinds of snails. However, it is also important to remember that some snails can be of benefit to your garden.
Giant African Snails (Lissachatina fulica)
Giant African snails are the goliaths of the snail world. Their shells can peak 70 mm (2.8 inches) above the ground. From tentacles to tail, adult giant African snails may extend 200 mm (7.9 inches) or more in length. These snails keep growing throughout their lives. This snail’s shell may be any of a number of shades of brown, depending on its diet, which includes plants of all kinds, fruits, vegetables, dead animals, bones, and even small stones and concrete. When plants are not available, these snails have been known to eat stucco off houses and bark off trees. Giant African snails (Lissachatina fulica) hide in the ground during the day and come out to feed at night. A tropical snail, they are killed by temperatures lower than about 8 degrees C (45 degrees F).
Giant African snails are hermaphrodites, each individual possessing both kinds of reproductive organs. They participate in an elaborate mating ritual that takes several hours, beginning with petting each other’s heads and ending with the larger snail serving as the female partner. Each snail can lay up to 400 eggs in a single clutch, up to 1200 eggs in a single year.
As their name suggests, giant African snails originated in Africa, specifically in East Africa. Giant African snails were taken to China in 1931. The US military took the snail to islands in the South Pacific to serve as a food source for troops, but it escaped and devastated the local snails. When the military introduced a second snail to control the giant African snails, it too turned out to be a predator on local plants – but not the giant African snail.
Three giant African snails were taken to Miami, Florida (illegally) in 1966 and released into a garden without knowledge of their potential danger to the environment. Within seven years, 18,000 giant African snails were captured in Miami alone, and the species has continued to invade America’s Gulf Coast region. In 1988, the snail was taken to Brazil and sold to would-be snail farmers. Most of the farms failed and the farmers threw the snails away. They multiplied are now found in 26 of Brazil’s 29 states.
Giant African snails are edible, but cooking them is something you should not try at home. That is because giant African snails host parasites that cause heartworm infections in dogs and people, meningitis in people, and whipworm infections in children. The whipworm causes trichuriasis, a chronic condition of abdominal pain, fatigue, and diarrhea that interferes with normal growth and intellectual development. Both the meat of the snail and its slime and feces carry parasites. Slime on unwashed raw vegetables can transmit disease.
It is illegal to own a giant African snail in the United States. Teachers are not permitted to keep them for biology classes. If you live in the USA, you are obligated to report giant African snails to your local USDA agricultural extension office so they can be safely removed from your property.