Slugs, soft-bodied gastropods related to snails, are commonly encountered in damp environments such as gardens. A long-standing piece of common knowledge suggests that applying salt to these creatures results in their demise. The interaction between salt and a slug’s physiology offers a clear illustration of a fundamental biological process.
The Immediate Observable Effects
When salt makes contact with a slug, the visual changes are rapid and pronounced. The slug’s body begins to shrivel and contract almost immediately, and the creature may writhe or attempt to move away from the salt granules. As this occurs, a significant amount of foamy or slimy mucus often appears around the slug’s body, giving the impression that it is “melting” away.
The Underlying Biological Process
The dramatic effect of salt on a slug is explained by osmosis, a fundamental biological process. Osmosis describes the movement of water molecules across a semi-permeable membrane from an area of higher water concentration to an area of lower water concentration. Slugs possess highly permeable skin, which allows for the easy exchange of water with their environment. When salt is applied, it dissolves in the thin layer of mucus on the slug’s skin, creating a highly concentrated salt solution outside its body.
This external high salt concentration means there is a lower concentration of water molecules outside the slug compared to the water-rich environment inside its cells and tissues. To achieve equilibrium, water rapidly moves out of the slug’s body and into the salt solution through its permeable skin. This process, known as dehydration, causes the slug’s cells to lose their internal water content. Unlike snails, slugs lack a protective outer shell, making them particularly vulnerable to this rapid and uncontrolled water loss.
Humane Slug Control Methods
Given the painful dehydration process caused by salt, many consider salting slugs an inhumane method of control. Fortunately, several more humane and effective alternatives exist for managing slug populations in gardens:
- Hand-picking slugs from plants, especially at night, and relocating them away from desired vegetation.
- Using beer traps, which attract slugs to the yeast in beer, causing them to drown in shallow containers buried in the soil.
- Creating physical barriers around plants, such as copper tape or wire, which provide a mild electric shock that slugs avoid.
- Encouraging natural predators like birds, frogs, toads, and hedgehogs to help keep slug numbers in check.
- Implementing cultural practices like watering in the morning to allow surfaces to dry before nightfall, or using organic slug pellets made from ferric phosphate.