Slugs are common garden pests. Many observe that sprinkling salt on these soft-bodied creatures causes them to shrivel and die, prompting the question: why does salt kill slugs?
The Science of Salt and Slugs
The primary reason salt is lethal to slugs involves osmosis. Slugs possess highly permeable skin, lacking a protective outer shell. Their bodies are composed of over 80% water. When salt is applied to a slug’s moist exterior, it rapidly dissolves in its mucus layer, creating a highly concentrated salt solution.
This external salt solution is hypertonic, meaning it has a higher solute (salt) concentration than the slug’s cells. Water moves from lower to higher solute concentration across a semi-permeable membrane to achieve balance. Consequently, water is rapidly drawn out of the slug’s cells and mucus layer through osmosis, attempting to dilute the external salt. This continuous outward flow leads to severe dehydration of the slug’s tissues.
Physical Effects on the Slug
The rapid water loss through osmosis triggers observable physical changes. As water is pulled from its cells, the slug’s body shrivels immediately. The slug also produces excessive mucus in an attempt to rehydrate or protect itself. However, this mucus is primarily water and contributes further to dehydration as water continues to be drawn out.
This intense dehydration causes the slug’s internal structures to collapse. The bubbling often observed is a result of gases escaping as the body rapidly desiccates. Ultimately, the severe and irreversible water loss leads to the breakdown of cellular functions and, within minutes, the death of the slug.
Practical Considerations and Alternatives
While effective, using salt for pest control has significant environmental drawbacks. Salt harms garden plants by inhibiting water and nutrient absorption, potentially leading to stunted growth, leaf damage, or death. It also alters soil composition, increasing salinity and negatively affecting beneficial soil organisms.
Due to potential harms to plants and the garden ecosystem, salt is not recommended for slug control. More environmentally friendly approaches exist for managing slug populations. These alternatives include physical barriers like copper tape or crushed eggshells, manual removal, or setting up traps such as beer traps. Encouraging natural predators like birds, hedgehogs, and certain beetles can also help keep slug numbers in check.