Snails and slugs are terrestrial gastropod mollusks that thrive in damp, sheltered environments across the globe. These slow-moving organisms are generally detritivores, consuming decaying plant matter, but they also feed on living vegetation. While they may appear to be harmless garden dwellers, their presence introduces specific, often serious, risks to human health, domestic animals, and cultivated plants.
Assessing the Threat to Gardens
These mollusks cause extensive damage to cultivated plants by feeding at night or during damp, overcast periods. They possess a rasping mouthpart called a radula, which is covered in thousands of microscopic teeth used to scrape and chew plant tissue. The damage typically manifests as irregular holes with smooth edges on leaves, especially in soft, tender foliage like seedlings and leafy vegetables. They can completely consume young sprouts or shred leaves, causing growth retardation or plant collapse. A characteristic indicator of their activity is the silvery, iridescent slime trail they leave on leaves, stems, and the ground. Plants like hostas, basil, lettuce, and strawberries are susceptible to their appetite.
Zoonotic and Parasitic Dangers to Pets
Snails and slugs act as intermediate hosts for several parasites that can cause serious illness in domestic pets, particularly dogs. The most prominent is the French Heartworm, Angiostrongylus vasorum, a nematode whose adults reside in the pulmonary arteries and right side of the heart of canids. Dogs become infected by accidentally ingesting the mollusk or its slime, which contains the infective larval stage. Infected dogs can develop cardiorespiratory symptoms such as chronic coughing, reduced exercise tolerance, and difficulty breathing. The parasite can also cause life-threatening blood clotting disorders, leading to uncontrolled hemorrhaging. Another serious, though geographically limited, threat is the Rat Lungworm, Angiostrongylus cantonensis, which causes neurological signs like spinal pain and ascending paralysis in dogs. Symptoms often include vomiting and diarrhea shortly after ingestion, followed by central nervous system issues approximately eleven days later.
Health Concerns for Humans
The primary health concern for humans involves the parasitic nematode Angiostrongylus cantonensis, commonly known as the Rat Lungworm. Humans are considered accidental hosts, contracting the infection by ingesting the parasite’s larvae. This ingestion occurs by consuming raw or undercooked snails and slugs, or by eating contaminated produce. The larvae are often transferred to vegetables, such as lettuce, when mollusks crawl over them, leaving infective larvae in their slime or feces. Once ingested, the larvae migrate from the gut to the brain and spinal cord, where their death triggers a severe inflammatory response. This condition is known as eosinophilic meningitis, characterized by symptoms that include intense headaches, neck stiffness, and neurological abnormalities. While most human infections are self-limiting, severe cases can lead to permanent brain damage or, rarely, death. Thoroughly washing all garden produce before consumption is the most direct preventative measure.
Safe Strategies for Control and Prevention
Managing mollusks effectively requires non-toxic methods that protect both pets and humans from chemical exposure.
Physical Barriers
One approach is the use of physical barriers, such as copper tape, which creates a mild electrical sensation when the mollusk’s slime reacts with the metal. Another common barrier is food-grade diatomaceous earth, which consists of microscopic, sharp fossilized remains that dehydrate the pests.
Cultural Controls
Cultural controls focus on making the garden less hospitable by reducing moisture and removing daytime hiding spots. Switching from overhead sprinklers to drip irrigation minimizes damp soil surfaces, and clearing debris or dense groundcover eliminates sheltered retreats.
Trapping and Removal
For trapping, iron phosphate baits are considered a safer alternative to metaldehyde, as iron phosphate is less toxic to pets and wildlife if inadvertently consumed. Manual removal after dark, when snails are most active, can significantly reduce the population over time.