Fascinating Mollusks: Giant African and New Zealand Land Snails
Two Giant Land Snails
The giant African land snail and the New Zealand Powelliphanta are huge animals compared to the common garden snail. They are both fascinating mollusks to observe and study, but unfortunately one is a potential pest and the other is endangered.
The giant African land snail may reach eight inches in length and four inches across - the size of a human fist. It's a herbivore with a very large appetite and can be a serious agricultural pest. It may also carry a parasite that causes meningitis in humans. The snail is long lived and may reach ten years of age.
Powelliphanta is a genus of carnivorous snails. The genus name is also used as a common name. A Powelliphanta is a large snail, but it's a little smaller than the giant African land snail. Snails usually move slowly, but the lunge of a Powelliphanta for its earthworm prey is sudden and rapid. The animal may live for twenty years, an amazingly long time for a snail. Unfortunately, many members of the genus are endangered.
Snails belong to the phylum Mollusca. The animals in this phylum are referred to as either mollusks or molluscs. The first term is the preferred one in North America while the second is preferred in the rest of the world.
The Giant African Land Snail and its Distribution
There are three species of mollusks from Africa that may be called giant African land snails: Achatina achatina, Lissachatina fulica (frequently known by its older scientific name of Achatina fulica) and Archachatina marginata. They each have a variety of common names, so it's often less confusing to refer to them by their scientific names.
The species most often found in the United States is Achatina fulica, which is sometimes called the giant African snail. It's native to East Africa but has been introduced to other areas of the world. Although the snail lives in a warm climate in its native country, it's a hardy animal. It survives cold weather and snow in the United States by hiding, slowing its metabolism and becoming sluggish or hibernating until warm weather returns.
Hector, the Giant African Snail
The giant African snail usually has a conical shell which is generally reddish brown with yellow bands. The shape varies, however, and the color depends on the conditions in the snail's environment. The soft part of the body is usually brown or tan. The snail can reach a length of up to eight inches without stretching its body.
The snail has two pairs of retractable tentacles on its head. The upper, longer pair bear the eyes and are also sensitive to touch. The lower, shorter pair provide the sense of smell as well as touch. Like its smaller relatives, the snail moves by secreting mucus or slime and then moving over the slime with its muscular foot. The foot is the large, soft structure at the base of the animal.
Achatina fulica as a Pet
Achatina fulica has a voracious appetite and eats at least 500 different kinds of plants in its native habitat. It lives on the edge of forests and in agricultural areas and may become a major pest. It eats fruits and vegetables when it can find them - including garden and agricultural crops - but will also eat ornamental plants.
The snails are very invasive when they are outside their natural habitat. They destroy both crops and property. They even eat stucco from houses. The stucco contains the calcium that the animals need to make their shells.
Achatina fulica Eating Lettuce
The giant African snail is a hermaphrodite, which means that it contains both male and female reproductive organs. It also means that every snail can lay eggs if it obtains sperm from another animal. During mating, sperm exchange takes place between a pair of snails.
Each snail lays 100 to 400 eggs. The eggs are small, white and round in shape. A snail can lay several egg clutches from one sperm exchange. The eggs are laid at two to three month intervals, which could result in at least 1200 eggs produced per animal each year.
Achatina fulica Laying Eggs
Introduction of Giant African Land Snails to the United States
Achatina fulica has been brought to the US both accidentally and deliberately. The snails may have arrived in cargo, hidden and unnoticed, but they have also been smuggled into the country. They are sold as pets and are kept in some schools, even though it's illegal to import or own a giant snail without a permit from the US Department of Agriculture. In some countries it's legal for anyone to keep the snail in their home.
In 1966, a boy living in Florida smuggled three snails into the country to keep as pets. His grandmother eventually set them free in the garden. After seven years, there were more than 18,000 giant African land snails in Florida, all resulting from this release. The eradication program required ten years and cost a million dollars. Unfortunately, as the video below shows, the snails have reappeared in Florida. They have the potential to be a very serious pest, attacking orchards and crops.
Giant Snails in Florida
There is a small chance that giant łand snails could transmit disease. The snails sometimes contain the larvae of a parasitic nematode known as the rat lungworm. The parasite causes meningitis in humans. This potentially serious disorder involves inflammation of the meninges, which are the membranes that cover the brain. The snails obtain the parasite by eating infected rat feces. If a snail was bred in captivity, is given clean food and has never been outdoors, it's unlikely to have eaten rat feces. Snails collected from the wild may contain the parasite, however.
If a snail contains the nematode, a person may need to eat the snail in a raw or undercooked form in order for the parasite to infect their body. Researchers don't yet know if the parasite can be transmitted in snail slime, although this is a distinct possibility. The researchers say that it's a good idea to wash our hands after we touch any snail (or one of its slug relatives) because the slime can transmit bacteria that cause disease.
A Powelliphanta Snail Catches an Earthworm
They (Powelliphanta) suck up earthworms like spaghetti.— New Zealand Department of Conservation
Powelliphanta Snails of New Zealand
Powelliphanta snails are also giants of the snail world and are found only in New Zealand. They are named after Arthur William Baden Powell. He studied the animals and separated them from a related group in the classification scheme for snails.
The shells of Powelliphanta snails may reach 3.5 inches in diameter. They are flatter and rounder than those of giant African land snails. The shells are often a mixture of yellow, gold, dark red, brown or black and are sometimes beautifully patterned.
Powelliphanta snails live in moist forests and are mainly nocturnal. They spend the day under leaves or logs in a dark, moist place. During the night they prey chiefly on earthworms, but they will also eat slugs and other invertebrates.
The soft parts of the snail are typically dark brown or black in color, but in November 2011 a snail with a golden brown shell and a pure white body was found. Biologists estimate that it was about ten years old. They were surprised that it had avoided being killed by predators for so long, since its body showed up very clearly against the background.
Powelliphanta snails have a much lower reproductive rate than giant African land snails. They are hermaphrodites and exchange sperm with another snail. One snail may produce five to ten eggs in a year - far fewer than the potential 1200 or more produced by the giant African land snail.
The eggs are pink and have a hard shell that resembles the shell of a bird's egg. They are relatively large in size and sometimes reach 14mm in length. Several months pass before the eggs hatch.
In snails, exchange of sperm and egg release occur through a pore on one side of the body near the head instead of from the rear end.
A Species of Powelliphanta
According to the New Zealand Government's Department of Conservation, there are at least 21 species and 51 subspecies of Powelliphanta snails. The survival of 40 species or subspecies is threatened by predation or habitat loss.
Possums are major predators of the snails. The possums were introduced to New Zealand and are now threatening many species of native wildlife. Rats, pigs, hedgehogs, thrushes and weka (large, flightless birds) also eat the snails. Destruction of forest in the past has meant that the snails now live in limited areas. There are still conflicts over land use near or in the snail's habitat.
Another potential problem for the snails is a phenomenon known as beech mast. The term refers to high levels of seed produced in beech forest. The seeds are eaten by snail predators, including rodents. An increased rodent population results, which in turn creates an increased threat to the snails.
The Future of the Snails
Giant African łand snails are very interesting animals, but they can definitely be pests. Their control is very important, but it would be a shame if they disappeared completely. Their history in the United States shows how problematic an introduced species can be.
Powelliphanta snails are also Interesting creatures, but most people wouldn't describe them as being cute. That's part of their problem. People are often concerned about endangered animals that are furry, feathery, clever or cute, but the fate of a snail doesn't worry them as much. In addition, the snails are usually active at night, when most people are unaware of them. Powelliphanta snails are unique animals. It would be very sad if they disappeared from the Earth.
© 2012 Linda Crampton