There are about 43,000 living snail species. Three of them have become invasive pests in China, Colombia, India, Barbados, Hawaii, and many other corners of the world: Achatina achatina, Archachatina marginata, and Lissachatina fulica (a.k.a. Achatina fulica)—a trio better known as giant African land snails. Native to East Africa, the snails can do a lot of damage when they’re introduced to foreign habitats. Here’s what you need to know about these monster mollusks.

1. Giant African land snail shells can be as big as a man’s fist.

Whorled, striped, and brownish overall, the shells can measure up to 8 inches long and nearly 5 inches in diameter. According to the USDA’s Animal and Plant Health Inspection Service, that’s “about the size of an average [human] adult fist.”

2. Oblivious pet owners helped the giant African land snails spread around the world.

India’s giant African land snail problem began in 1847. Some of the pioneering snails were probably hitchhikers that entered the subcontinent on shipments of timber. Others got an assist from exotic animal-lovers; a blacksmith who reportedly kept L. fulica as pets may have helped them invade the Indian state of Bihar during the 1960s.

Giant African land snails made their way to Florida in 1966, when a boy brought three of the snails home from a trip to Hawaii, where they were already invasive. His grandmother later set them free.

3. Invasive giant African land snails are bad news for farmers.

Peanuts, cucumbers, cocoa, and peas are just some of the commercial crops that giant African land snails devour. They can eat over 500 kinds of plants, including lichens, algae, and fungi.

4. Stucco and concrete are also on the giant African land snails’ menu.

Giant African land snails may be predominantly herbivorous, but their shells need a steady supply of calcium to grow. To get it, the snails feed on bones, eggshells, oyster shells, and the shells of other snails. They’ll even eat human-made calcium sources like stucco, concrete, and paint—much to the horror of homeowners.

5. Giant African land snails can carry dangerous parasites.

The rat lungworm (Angiostrongylus cantonensis) uses snails to complete its life cycle. The adult worms both live and reproduce inside common rat species, such as black, brown, and cotton rats. The worm’s larvae end up in the host mammal’s poop and are eventually excreted. The feces are then eaten by scavenging snails. If one of the worm-carrying snails is later eaten by a rodent, the cycle continues.

A 2015 survey of 50 L. fulica snails collected in Miami found that 18 of them harbored rat lungworms. The worms can cause eosinophilic meningitis in humans who eat the snails, either as part of a meal or by accidentally ingesting parts of the snails on grocery store produce. The illness can be fatal.

6. Giant African land snails are hermaphroditic.

The giant snails have female and male reproductive organs and are prolific breeders. One instance of mating can fertilize several clutches of eggs over a period of time. Because a single snail can produce 1200 eggs per year, giant African land snails can take over an environment quickly.

7. Giant African land snails can flatten your tires.

Run over these invertebrates at your own risk. Their tough, sharp shells can blow out car tires—or turn into flying shrapnel when accidentally crushed by a lawnmower.

8. It took seven years and $1 million to get rid of giant African land snails in Florida …

Following their accidental introduction in 1966, giant African land snails practically took over south Florida. The state spent more than $1 million and surveyed nearly a million properties to find and eliminate them. The effort paid off: Over the next seven years, more than 18,000 specimens were wiped out. In 1975, Florida’s Department of Agriculture and Consumer Services announced that the invasive giant snails had been fully eradicated [PDF].

9. … But the giant African land snails weren’t done with the Sunshine State.

The snails came back in 2011, likely in an illegal shipment intended for religious purposes. They first popped up in Miami-Dade County, then spread into neighboring Broward County. This time around, the state spent more than $24 million to get rid of them, and no new sightings have been reported in Florida since 2017. In October 2021, the snails were again declared eradicated by the state’s agriculture commissioner.

10. Trained dogs helped find the giant African land snails.

Labrador retrievers trained by the USDA were enlisted to sniff out the invasive pests. Some dogs found literally hundreds of the snails per week. Assisted by the puppers, Florida officials were able to find and eliminate more than 168,000 snails in the state’s most recent campaign.