Snails frequently cause frustration by consuming tender plants. Their soft bodies and reliance on moisture make them susceptible to a variety of deterrents and lethal measures. These methods range from simple habitat modifications and physical barriers to chemical controls and the introduction of natural predators.
Physical Barriers and Environmental Conditions
Snails are gastropods that require high levels of moisture to move and breathe. They are most active at night or during damp weather, retreating during the day to cool, moist hiding spots like under boards, dense ground cover, or garden debris. Removing these daytime refuges is a simple form of environmental control that exposes them to desiccation, which is rapid water loss.
One of the most effective non-chemical barriers is copper, which creates an electrochemical reaction when contacted by the snail’s mucus. The snail’s slime trail contains ions that react with the copper metal, generating a tiny electrical charge. This reaction is uncomfortable for the mollusk, causing it to retreat from the copper strip.
Abrasive or desiccating materials are also used for control. Diatomaceous earth, composed of the fossilized remains of microscopic organisms, works by damaging the snail’s protective outer layer, leading to fatal dehydration. However, this powder loses its effectiveness quickly when it becomes wet. Crushed eggshells are often suggested as a barrier, but the mollusk’s thick mucus layer often allows it to glide over such gritty materials with little lasting effect.
Scents and Tastes Snails Avoid
Snails use a highly developed sense of chemoreception to navigate and find food, making them sensitive to strong odors and unpalatable tastes. Substances with pungent essential oils or high concentrations of certain compounds can act as powerful sensory deterrents.
Caffeine is one of the most studied repellent and lethal agents, with strong solutions acting as a neurotoxin. Research shows that a 1% to 2% caffeine solution can be lethal, rapidly affecting the snail’s central nervous and cardiovascular systems. Even weaker solutions, such as a spray made from brewed coffee, can deter feeding by making the treated foliage unpalatable.
Garlic is another effective repellent, relying on the sulfur compound allicin, which is released when the bulb is crushed. Allicin is toxic to snails and can be applied as a spray barrier around vulnerable plants. Furthermore, plants with strong aromatic properties, such as rosemary, thyme, chives, and mint, are often avoided because the resinous chemicals in their leaves deter gastropod feeding.
Natural Predators
Introducing or encouraging natural enemies is a long-term, ecologically sound method for managing snail populations. These predators provide continuous control without the need for chemical intervention.
Ground-foraging birds, such as thrushes and blackbirds, are particularly effective predators. Song thrushes are known for smashing snail shells on an anvil-like stone to access the soft body. Domestic ducks, especially the runner varieties, are also voracious consumers of snails and slugs and can be used for pest control in gardens.
In the insect world, predatory ground beetles and firefly larvae actively hunt and consume snails and slugs. Microscopic organisms called parasitic nematodes can also be used as a biological control agent. These worms are applied to the soil and enter the mollusk’s body, infecting it with bacteria that cause death. Amphibians like frogs and toads will also readily consume smaller snails as part of their diet.
Molluscicides and Lethal Baits
The most aggressive control methods involve baits and chemicals designed to kill the snails. Modern molluscicides often use iron phosphate as the active ingredient, which is considered safer than older chemicals like metaldehyde. Once ingested, iron phosphate interferes with the snail’s calcium metabolism, causing it to stop feeding and die within a few days. However, some commercial formulas contain EDTA, a chelating agent that makes the iron more toxic, which can pose a risk to pets if consumed in large quantities.
A simple and attractive bait is a beer trap, which capitalizes on the snails’ attraction to the yeast in the fermenting liquid. A shallow dish sunk into the ground and filled with beer will attract snails. They then fall in and drown, but this method requires frequent emptying and refilling to remain effective.
While highly lethal, common table salt should be used only with extreme caution or avoided entirely in the garden. Salt kills snails instantly through osmosis, rapidly drawing all the water out of their bodies. However, salt is highly detrimental to soil health; it increases salinity, draws water out of plant roots, and can sterilize the soil by killing beneficial microorganisms and earthworms.