Giant African and New Zealand Land Snails: Fascinating Mollusks
Two Giant Snails
The giant African land snail and the New Zealand Powelliphanta are huge animals compared to common garden snails. They are fascinating mollusks to observe and study, but unfortunately one is a potential pest and the other is either threatened or endangered, depending on the species.
The shell of the giant African land snail species found in the United States may reach more than eight inches in length. The animal is a herbivore with a very large appetite and can be a serious agricultural pest. It may sometimes carry a parasite that causes meningitis in humans. The snail is long lived and can reach ten years of age. In some places, it's kept as a pet.
Powelliphanta is a genus of carnivorous snails. The genus name is also used as a common name. The largest species may be as big as a fist. 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.
Snails belong to the phylum Mollusca and the class Gastropoda. The animals in the phylum are referred to as either mollusks or molluscs. The first term is preferred in North America while the second seems to be preferred in the rest of the world.
The Giant African Land Snail
Three species of mollusks from Africa may be called a giant African land snail: Achatina achatina, Lissachatina fulica (frequently known by its older scientific name of Achatina fulica), and Archachatina marginata. The species have a variety of common names, so it's often less confusing to refer to them by their scientific names. They belong to the same biological family, which is known as the Achatinidae.
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.
A Pet Giant African Land Snail
Giant African Land Snails are sometimes referred to as GALS. The term is used in both the singular and the plural.
The giant African snail generally has a conical shell that is reddish brown with yellow bands. The shape varies, however, and the colour depends on the conditions in the animal's environment. The soft part of the body is usually brown or tan. An adult Achatina fulica sometimes reaches a length of eight inches without extending its body. It's not the biggest snail in its category that has been observed, however, as the quote below shows.
The animal 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.
The largest known land gastropod is the African giant snail Achatina achatina, the largest recorded specimen of which measured 39.3 cm (15.5 in) from snout to tail when fully extended, with a shell length of 27.3 cm (10.75 in).— Guinness World Records
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.
Meal Time for a GALS
The giant African snail is a hermaphrodite, which means 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 animal 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. The young animals that hatch from the eggs are tiny, but they grow fast.
The videos in this article are shared for general interest. I've never had a GALS as a pet. I don't know whether the treatment of the pets in the videos is appropriate for keeping a snail healthy and comfortable. If you live in a place where keeping the snail as a pet is legal and you want to own one, you should explore how to care for it.
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 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 animals have reappeared in Florida. They have the potential to be a very serious pest, attacking orchards and crops.
A Problematic Mollusk in Florida
According to a linked distribution map on the website of the Everglades Cooperative Invasive Species Management Area, wild giant land snails were still present in Florida in 2017. In 2019, the website still referred to them as a pest in certain parts of the state.
Possible Disease Transmission
There is a small chance that giant łand snails could transmit disease. The animals sometimes contain the larvae of a parasitic nematode known as the rat lungworm (Angiostrongylus cantonensis), though the CDC says that it's unknown if the GALS in the United Stated contain the parasite. The larvae can cause meningitis in humans. This disorder involves inflammation of the meninges, which are the membranes that cover the brain. The condition may not be serious, but it sometimes is.
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. Animals collected from the wild might contain the parasite, however.
The disease is transmitted by other snails as well as GALS. If a snail contains the nematode, a person will probably need to eat the mollusk in a raw or undercooked form in order for the parasite to infect their body. I've seen no evidence supporting the idea that the parasite can be transmitted by slug slime. It's probably a good plan to wash the hands after handling a snail or a slug, though. People often decide to do this due to the slime deposit on the skin.
Unlike GALS, Powelliphanta snails generally aren't kept as pets. They are large snails when fully grown and have at least one interesting characteristic of their own. Their method of catching and eating earthworms is impressive.
A Powelliphanta Engulfs 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 (1901–1987). Powell was a malacologist (a scientist who studies mollusks) and worked at the Auckland Museum. He studied the snails and separated them from a related group in the classification scheme. The animals are classified in the family Rhytididae.
The largest species in the genus is Powelliphanta superba prouseorum. According to the New Zealand Government's Department of Conservation, or DOC, the animal can grow as big as a fist and has a shell up to 9 cm (3.5 inches) across.
The shells of Powelliphanta snails are flatter and rounder than those of giant African land snails. They are often a mixture of yellow, gold, dark red, brown, or black and are sometimes beautifully patterned.
The soft parts of the snail are typically black, dark brown, or grey in colour. In November, 2011, an albino animal 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 its background.
Habitat and Diet
Powelliphanta snails live in moist lowland forests, high-altitude forests, or areas with alpine tussock, depending on the species. Tussock grasses grow in bunches, unlike the grass that we use for lawns. The species that live in alpine areas have to deal with very cold winters.
The snails are mainly nocturnal. They spend the day in a dark and moist environment, such as in crevices or under leaves or logs. During the night, the animals prey chiefly on earthworms on the forest or grassland floor. They also eat slugs and other invertebrates.
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. This is due to a phenomenon known as torsion. During larval development, parts of the animal's body rotate 180 degrees with respect to the head and foot.
Powelliphanta snails have a much lower reproductive rate than giant African land snails. They are hermaphrodites and exchange sperm with another snail. One animal 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 that of a bird's egg. They are relatively large in size and sometimes reach 12 mm in length. Several months may pass before the eggs hatch.
A Huge New Zealand Mollusk
According to the DOC, at least 16 species and 57 subspecies of Powelliphanta snails exist. 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, wild pigs, hedgehogs, thrushes, and weka (large, flightless birds) also eat the snails.
One 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.
Destruction of forest in the past has meant that Powelliphanta snails now live in limited areas. There are still conflicts over land use near or in the animal's habitat. Drainage of land and damage by livestock have been problems.
In some areas, open-cast coal mining is threatening the snail's existence. Powelliphanta augusta was discovered in a limited area after mining had been in progress for some time. Some snails were brought into captivity and others moved to new habitats. It's not yet known whether the latter transfers will save the species. It's adapted for success in the specialized habitat where the coal is mined.
A Powelliphanta Versus an Earthworm
A Possible Public Relations Problems
Powelliphanta snails are 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.
The Future of the Snails
Although giant African łand snails are interesting animals and are admired as pets by some people, they can be annoying pests. Their control is very important. It would be a shame if they disappeared completely, though, as long as they are living in a place where they aren't causing harm. Their history in the United States shows how problematic an introduced species can be.
Powelliphanta snails are less visible due to their nocturnal habits, but like GALS they are interesting animals. They are an important contributor to their ecosystem and nature's diversity. I hope that the species and subspecies that are in trouble survive.
- An invasive giant snail in Florida from The Washington Post
- Giant African snail facts from the Everglades Cooperative Invasive Species Management Area
- Largest snail in the world from Guinness World Records
- Facts about angiostrongyliasis from the CDC (Centers for Disease Control and Prevention)
- Powelliphanta information from the New Zealand Department of Conservation
- Hunting for Powelliphanta marchanti from the Department of Conservation
- Why snail extinction matters from Scientific American
Questions & Answers
© 2012 Linda Crampton