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Whenever there is a species invasion, our diners will always joke: what are you afraid of? Eat it to extinction. But if you want to taste this lovely-looking and delicious invasive creature, the African snail, you might as well read this article before making a decision.

I don't know if you have ever heard such a story. I heard that eating snails raw is very helpful. My husband carefully fed several big snails with vegetables in his garden, ready for the whole family to enjoy. However, the price of delicious delicacies is unbearable. Soon, the family developed symptoms such as fever, severe headache and vomiting. In the end, the husband and wife, the eldest son and the husband's mother died, and the second son died after more than ten years in bed.

Such an accident, which can be called the "door-killing tragedy", may have made many people know the lovely and generous-looking African snails (Lissachatina fulica, also known as agate snails), which are the "well-fed snails" in this story. They always carry brown snail shells with yellowish stripes. The giant snail, which can grow to 20cm, is the largest snail in the world and one of the most threatening invaders.

A large African snail with a tan shell on the back of ▲ (photo: Pixabay)

Large African snails are so destructive that they can feed on more than 500 plants, including fruits, vegetables and other crops as well as ornamental plants. But apart from the harm to agriculture and natural vegetation, more importantly, it will also threaten human life.

The body, feces, and even surface mucus of African snails carry a large number of germs and parasites. The real culprit behind the opening story is the most common parasite in African snails, Angiostrongylus cantonensis (Angiostrongylus cantonensis).

People and animals may be infected with Angiostrongylus cantonensis after contact with snail mucus, snails infected with parasites (or undercooked snails), or vegetables contaminated with snail mucus. Once it enters the human body, it may invade the brain through the central nervous system, causing symptoms such as fever, headache, neck stiffness, nausea and vomiting, and even death.

In fact, the most important host of Angiostrongylus cantonensis is not snails. They are mainly parasitic on the blood vessels in the lungs of mice. After spawning in the lungs of mice, they develop into first-stage larvae and are excreted in the feces. After being swallowed by molluscs such as slugs, snails and freshwater snails, the larvae develop into the third stage larvae in these intermediate hosts. The rodents prey on the molluscs, and the parasites return to where they breed.

The picture on the left shows two female Angiostrongylus adults isolated from the lungs of mice, with a unique spiral pattern of a white uterine tube and a red intestinal tract filled with blood; on the right, the third stage larvae of Angiostrongylus isolated from slugs. (photo source: DPDx / CDC)

It can be said that Angiostrongylus cantonensis travels smoothly between the final host and the intermediate host, and humans are only abnormal hosts mistakenly entering this cycle, because Angiostrongylus cantonensis usually cannot develop into adults in the human body. However, in recent years, cases of Angiostrongylus cantonensis infection are common. For one thing, it has a very high infection rate in snails (especially the protagonist and Fushu snail in this article). Second, the African snail has a strong ability to survive and reproduce, and has a large "population" in the south of China. Of course, the most fundamental reason is that humans take the initiative to eat them in an unsafe way.

"intentional" damage if the African snail, as a "porter" of germs and parasites, can be seen as unintentional to human beings, then its damage to the environment is "intentional". The African snail has a very good appetite, and its diet includes not only many crops of economic value to humans, such as broccoli, papaya and bananas, but also lichens, fungi and other snails (usually the carcasses of other snails).

If you look closely at the process of snails eating, you will find that although they move slowly, they are absolutely standard "dry snails" when they eat. In areas infested by African snails, vegetables grown by residents in their gardens can sometimes be eaten overnight.

Amazingly, the snail is actually the creature with the most teeth in the world. In its pinpoint-sized mouth, more than 20, 000 teeth are densely arranged on the banded tongue, so their tongues are called radula. In fact, the snail can not "gnaw", can only use the "grinder" general tongue teeth to rub the food off.

Even so, the feeding ability of large African snails is shocking. We often joke that we are going to eat dirt this month. The reality is that big African snails can not only eat soil, but can even lick and digest cement. Because they need a constant supply of calcium to maintain the growth of the huge, hard snail shell on their back, they usually consume a lot of plants to get calcium. Once plants can not meet the demand, they will feed on sand and cement, and sometimes even destroy human buildings, causing huge economic losses.

Survival and reproduction however, the destruction of the environment is only one of the self-cultivation of invasive species, and strong survivability in invasive areas is also a necessary condition.

As can be seen from the naming, the natural habitat of the African snail was originally in warm and humid Africa. But if the environment is too dry or cold, they can drill part of the software into the soil to slow down metabolism, which can last as long as 5 to 9 months. Sometimes they secrete milky mucous membranes to seal the shell and "close the door" for themselves. Combined with the fact that they are not picky about eating, the big African snails brought to warm areas are like a fish in water.

In addition, the African snail is usually able to reproduce when it reaches 6 months old. It is a hermaphroditic, heterogamous species. This means that each snail does not have to look for the "other half" of a particular sex to meet, as long as any two sexually mature snails meet, they can reproduce. Studies have shown that ideally, a large African snail can lay thousands of eggs in a lifetime, and the survival rate of offspring is close to 90%. This shows its strong reproductive ability.

Invasion and extermination due to the preference for warm climate, African snails are usually distributed between the Tropic of Cancer. In China, they mainly invade South China, while in the United States, Florida is troubled. In the 1960s, several large African snails were brought to Florida, which opened the way for hegemony.

According to the Florida Department of Agriculture and Consumer Services (Florida Department of Agriculture and Consumer Services,FDACS), after the pest was first discovered in 1969, Florida spent nearly $1 million to kill more than 17000 snails, and finally announced the eradication of the invasive creature in 1975. However, in 2011, Florida began a decade-long killing of a large African snail, which cost about $23 million to kill hundreds of thousands of snails and was finally declared a success in 2021. Unfortunately, in June this year, Florida once again discovered a large African snail and was forced to start the third "cochlear war".

It can be said that Florida has a lot of experience in fighting the African snail. In the second killing operation, FDACS called on residents who saw large African snails to take the initiative to report by telephone and successfully tracked and eliminated a large number of snails. They also spray insecticide tetraacetaldehyde (Metaldehyde) against snails and slugs to achieve targeted killing. They even trained Labradors that can sniff out large African snails and track them at night when they are most active. In addition, although snails move slowly, they can use mucus to attach to moving vehicles, garbage, etc., and spread around. Therefore, it is critical to set up a quarantine zone and strictly check the soil, machines and so on that may take the snail out of the quarantine zone.

Humans have made great efforts to eradicate the African snail, but the African snail is not aware of the harm it has caused to human beings. In fact, apart from the mating process, they are lonely all their lives, neither communicating with their peers nor establishing any connection with their offspring. All their lives, they are either moving, eating or resting.

When you encounter a traveling snail, please let it be beautiful alone, do not touch, do not raise, do not eat.

Reference link:

Https://arstechnica.com/science/2022/07/florida-battling-giant-savage-snails-that-spread-brain-invading-worms-again/

Https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.509.1061&rep=rep1&type=pdf

Https://animaldiversity.org/accounts/Achatina_fulica/

Https://www.cbsnews.com/news/giant-snails-the-size-of-your-foot-are-terrorizing-florida/

Https://www.fdacs.gov/Agriculture-Industry/Pests-and-Diseases/Plant-Pests-and-Diseases/Invasive-Mollusks/Giant-African-Land-Snail

Https://www.cdc.gov/parasites/angiostrongylus/index.html

Https://nhm.org/stories/microscopic-look-snail-jaws

This article comes from the official account of Wechat: global Science (ID:huanqiukexue), written by: not weekly revision: 27

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