While most snails are harmless, certain species can be dangerous. The term “poisonous” in this context refers to organisms that can cause harm through direct contact, stinging, or ingestion. This article clarifies how some snails can be harmful and identifies which species present risks.
How Snails Can Be Toxic
Snails can become toxic through several distinct biological mechanisms. Some actively produce and inject venom, a complex mixture of neurotoxins designed for subduing prey and defense. These venoms can act rapidly on the nervous system, leading to paralysis or other severe effects.
Other species become toxic by accumulating poisonous substances from their environment through their diet. This process, known as bioaccumulation, occurs when snails consume toxic algae, plants, or absorb heavy metals and pesticides. The ingested toxins are then stored within their tissues, potentially harming any animal that consumes the snail. Furthermore, some snails serve as intermediate hosts for parasites that can cause illness in humans if consumed raw or improperly handled.
Dangerous Marine Snails
Among the most dangerous snails are certain marine species, particularly those that employ venom. Cone snails (family Conidae) are a notable example, found primarily in tropical and subtropical waters, including coral reefs and sandy bottoms. These predatory snails possess a specialized, harpoon-like tooth (radula) which they extend to inject potent venom into prey or perceived threats.
The venom of cone snails contains diverse neurotoxins (conotoxins) that disrupt nerve function. A sting from a larger cone snail can range in severity from mild pain and numbness to paralysis and, in rare cases, even death, depending on the species and venom amount. Their attractive, patterned shells can tempt unsuspecting individuals to pick them up, increasing the risk of a sting. While cone snails are well-known for their potent venom, other marine snails, such as some whelks, can also accumulate toxins from their diet, making them unsafe for consumption.
Risks from Land and Freshwater Snails
Land and freshwater snails generally do not possess venom, but they can still pose significant health risks, primarily as carriers of parasites. They can transmit parasites like the rat lungworm (Angiostrongylus cantonensis). Humans become infected by ingesting raw or undercooked snails, or by consuming produce contaminated with snail slime or small, unnoticed snails. The parasite can then migrate to the brain, causing eosinophilic meningitis, a serious condition.
Another parasitic threat involves schistosomes, trematode worms that cause schistosomiasis (snail fever). Freshwater snails act as intermediate hosts for these parasites, releasing larval forms into the water that can penetrate human skin upon contact. Land and freshwater snails can also absorb environmental contaminants such as heavy metals and pesticides. Consuming snails that have accumulated these toxins can lead to poisoning.
Safe Practices Around Snails
Exercising caution around snails, particularly unfamiliar species, is prudent to minimize risks. When encountering marine snails, especially in tropical waters, avoid touching or picking them up. Even seemingly empty shells of cone snails can pose a threat, as the animal inside might be alive and capable of stinging. Observe these creatures from a distance.
For land and freshwater snails, prioritize food safety. Thoroughly wash produce, especially leafy greens, to remove small snails or their slime trails, which could carry parasites. Never consume raw or undercooked land and freshwater snails to prevent parasitic infections. While most snails are harmless, these precautions help ensure safety.