Slugs are common garden inhabitants, often found on damp surfaces. A common belief involves using salt to deter or eliminate them. This method triggers a biological reaction in these soft-bodied creatures, leading to a rapid effect.
The Immediate Impact of Salt
When salt makes contact with a slug’s moist skin, the changes are immediate and striking. The slug begins to writhe and contort, often appearing to shrink or “dissolve” as it produces an excessive amount of bubbly slime. This visible reaction is a direct consequence of rapid water loss from the slug’s body. Within minutes, the slug can shrivel significantly, leaving behind a residue that might resemble foam. This transformation highlights the intense physiological stress the slug experiences.
The Science of Dehydration
The dramatic effect of salt on a slug is explained by osmosis. Slugs possess soft, permeable skin, lacking protective outer layers like a shell. Their bodies are composed of a high percentage of water. When salt is sprinkled on a slug, it rapidly dissolves in the thin layer of moisture on its skin, creating a highly concentrated salt solution outside the slug’s body.
This external high-salt concentration creates an osmotic gradient. Osmosis is the passive movement of water molecules across a semi-permeable membrane—like the slug’s skin—from an area of higher water concentration to an area of lower water concentration. Water rapidly moves out of the slug’s cells and into the salt solution on its exterior. This continuous outward flow of water leads to severe and rapid dehydration, causing the slug’s cells to collapse and ultimately leading to its death.
Ethical Considerations and Other Methods
While effective at eliminating slugs, the use of salt raises ethical concerns due to the painful and slow nature of the slug’s death. Rapid dehydration, which can take minutes, causes significant distress to the slug. Many consider this method inhumane. Gardeners often seek more humane or environmentally friendly alternatives for slug control.
- Physical barriers, such as copper tape or crushed eggshells, can deter slugs from reaching plants.
- Hand-picking slugs, especially at night when they are most active, provides a direct and immediate removal method.
- Attracting natural predators like birds, frogs, toads, and hedgehogs to the garden can help manage slug populations.
- Specific slug baits containing iron phosphate are available; these are considered less harmful to other wildlife compared to traditional chemical baits.