Snails are often perceived as slow, innocuous creatures, commonly found gliding through gardens or along sidewalks after a rain. While many terrestrial species are harmless to humans in a direct physical sense, certain types of snails can pose significant risks. These risks range from venomous stings to serving as carriers for serious diseases, affecting humans, pets, and garden ecosystems.
Direct Physical Threats from Snails
While common garden snails do not bite or sting and pose no direct physical threat, marine cone snails are a notable exception. These predatory gastropods, found in tropical waters, employ a venom delivery system. They utilize a harpoon-like tooth to inject a potent cocktail of neurotoxins, known as conotoxins, into their prey or as a defense mechanism.
The effects of a cone snail sting on humans vary depending on the species and venom amount. Initial symptoms include a sharp pricking sensation, localized pain, numbness, and tissue damage at the sting site. More severe envenomations, particularly from fish-hunting species like Conus geographus, can lead to systemic effects such as muscle weakness, respiratory paralysis, vision changes, and even cardiovascular collapse or coma. Fatalities, though rare, have been reported, sometimes occurring within one to five hours if untreated.
Snails as Disease Carriers
Snails can act as intermediate hosts for various parasites, posing a more widespread health concern than direct physical threats. Two prominent examples of diseases transmitted through snails are rat lungworm and schistosomiasis.
Rat Lungworm Disease
Rat lungworm disease, or angiostrongyliasis, is caused by the parasitic nematode Angiostrongylus cantonensis. The parasite’s life cycle involves rats as definitive hosts, where adult worms reside in their pulmonary arteries and pass larvae in their feces. Snails and slugs become intermediate hosts by ingesting these larvae, which then mature within them to an infective stage.
Humans can become infected by consuming raw or undercooked infected snails or slugs, or by ingesting produce contaminated with small, infected mollusks or their slime. Once ingested, the larvae migrate to the human brain or spinal cord, causing eosinophilic meningitis. Symptoms include severe headaches, stiff neck, tingling or painful sensations in the skin, low-grade fever, nausea, and vomiting. In some cases, neurological symptoms can progress to severe debilitation, coma, or even death.
Schistosomiasis
Schistosomiasis, also known as snail fever, is a parasitic disease caused by blood flukes of the genus Schistosoma. This disease is prevalent in tropical and subtropical regions, particularly in Africa, where an estimated 90% of those requiring treatment reside.
The parasite’s life cycle involves freshwater snails, which release larval forms called cercariae into the water. Humans become infected when these cercariae penetrate their skin during contact with contaminated freshwater sources, such as during swimming, bathing, or agricultural activities. Adult worms then develop within the human body, and their eggs are passed in feces or urine, completing the cycle if they reach freshwater inhabited by specific host snails.
Acute schistosomiasis can present with flu-like symptoms, including fever, chills, cough, muscle aches, and abdominal pain. Chronic infections can lead to significant organ damage, such as liver and spleen enlargement, intestinal issues, kidney damage, and bladder cancer.
Risks to Pets and Gardens
Beyond human health, snails can also pose risks to domestic animals and significantly impact garden and agricultural environments. These concerns relate to both parasitic infections and direct damage to plant life.
Pets
Domestic animals, particularly dogs, are susceptible to rat lungworm infection, similar to humans. Dogs can become infected if they ingest snails or slugs carrying the parasitic larvae. The migrating larvae can cause neurological signs, including spinal pain, hyperesthesia, and ascending paralysis. The disease’s severity depends on the number of larvae ingested; while some cases are mild, others can lead to serious neurological dysfunction.
Gardens
In gardens and agricultural settings, snails and slugs are notorious for the damage they inflict on plants. They are generalist feeders that consume a wide variety of plant material, creating irregular holes with smooth edges in leaves, stems, flowers, and fruits. Young seedlings and tender new growth are especially vulnerable to their rasping mouthparts, and entire plants can be defoliated overnight. The presence of silvery slime trails indicates their activity. This feeding behavior can lead to crop loss and diminished plant vigor for gardeners and farmers.
Minimizing Exposure to Snails
Reducing the potential risks associated with snails involves adopting practical habits, particularly concerning food preparation and environmental management. These measures focus on limiting contact with potentially infected mollusks and their habitats.
Thoroughly wash all fruits and vegetables under running water, especially leafy greens, to dislodge any small snails, slugs, or their slime. Avoid consuming raw or undercooked snails and slugs, as cooking them to appropriate temperatures eliminates parasitic larvae. When traveling to areas where schistosomiasis is prevalent, avoid direct contact with freshwater sources like rivers, lakes, and ponds. If access to safe water is limited, boiling water for at least one minute before bathing or drinking can help neutralize potential contaminants.
In garden environments, several practices can discourage snail populations:
Maintain good garden hygiene by removing debris, leaf litter, and excessive mulch to reduce hiding places.
Water plants in the morning rather than the evening, allowing the soil surface to dry before nightfall when mollusks are most active. Drip irrigation systems can also minimize overall moisture.
Use physical barriers such as copper tape around plant beds or a sprinkle of diatomaceous earth to deter snails.
Hand-pick snails from plants, especially at dusk.
Use simple traps like shallow containers filled with beer to manage their numbers.
Wear gloves while gardening to provide a barrier against potential contact with snail slime.