Snails are often seen as garden pests due to their feeding habits on plants. Many gardeners use salt to eliminate these soft-bodied creatures. This approach involves specific biological principles that explain its effectiveness.
Snail Body Structure
Snails possess a unique anatomy that makes them vulnerable to environmental changes, especially those involving moisture. Their soft, unsegmented bodies lack the protective outer layer, like the exoskeleton of insects. Instead, their entire external surface is highly permeable, meaning substances can easily pass through it.
A prominent feature of snails is their mucus layer, a gelatinous secretion covering their body. This mucus is mostly water, ranging from 91% to 98% water by weight, combined with glycoproteins. The mucus serves multiple purposes, including facilitating movement by reducing friction, allowing them to glide across surfaces, and assisting with adhesion. This mucus layer also plays a part in maintaining the snail’s hydration, as it traps water and helps shield the soft tissues from desiccation. However, this reliance on a permeable body surface and a water-rich mucus layer creates a significant weakness.
The Process of Osmosis
Understanding how salt affects snails requires a grasp of osmosis, a fundamental biological process. Osmosis describes the movement of water molecules across a semi-permeable membrane, which allows water to pass through but restricts the movement of larger dissolved substances, or solutes. Water naturally moves from an area where its concentration is higher to an area where its concentration is lower. This movement aims to equalize the concentration of solutes on both sides of the membrane.
If a semi-permeable membrane separates a low-salt solution from a high-salt solution, water molecules will move from the low-salt side to the high-salt side to dilute the more concentrated solution. This creates osmotic pressure, driving this water movement. Cells, including those of snails, maintain an internal balance of water and solutes, with their cell membranes acting as semi-permeable barriers regulating this delicate equilibrium.
Salt’s Impact on Snails
When salt comes into direct contact with a snail’s permeable skin and mucus, it creates a significant concentration difference. The salt crystals dissolve in the moisture on the snail’s body, forming a highly concentrated solution outside the snail. This external environment becomes hypertonic, meaning it has a much higher solute concentration compared to the water-rich cells and tissues inside the snail.
Due to the principles of osmosis, water is rapidly drawn out of the snail’s body. The water molecules within the snail’s cells and the mucus layer move through the permeable skin towards the higher salt concentration outside, attempting to dilute the external solution. This rapid water loss leads to severe dehydration, essentially drying out the snail. The snail’s internal systems collapse as its cells shrivel, resulting in the creature’s death. The visible bubbling observed is a result of the snail’s body expelling air and mucus as it rapidly loses fluid and shrivels.