Slugs are soft-bodied, terrestrial mollusks, related to snails but lacking a shell. These gastropods use a muscular foot to glide along on a layer of protective mucus, often moving under the cover of darkness or damp weather to prevent desiccation. Their mouth contains a specialized feeding organ called the radula, a ribbon of tiny teeth used for scraping and cutting food. Slugs are generalist feeders with a highly varied diet.
The Varied Natural Diet of Slugs
Slugs primarily function as omnivorous scavengers and detritivores in natural settings. Their natural diet centers heavily on consuming decaying organic matter, which facilitates nutrient cycling and soil health.
They regularly consume dead leaves, rotting wood, and other plant debris found on the forest floor or in garden soil. Slugs also feed opportunistically on fungi, including wild mushrooms, and graze on algae films that grow on surfaces. Less commonly, they may consume animal droppings, carrion, or small invertebrates like earthworms or other slugs.
Dietary Preferences and Garden Targets
While their natural diet is focused on decomposition, slugs readily shift their attention to live vegetation when it is available, particularly in cultivated areas. Slugs exhibit a strong preference for plant tissues that are soft, succulent, and high in moisture content. This preference explains why tender new growth and young seedlings, which lack tough cell walls, are especially vulnerable to damage.
Specific garden plants are targeted because they offer the ideal combination of texture and hydration. Highly favored items include lettuce, basil, cabbage, and the tender leaves of hostas. Ripening fruits that rest on the ground, such as strawberries and tomatoes, are also frequently attacked because of their soft texture and sugar content. Slugs use their radula to rasp away at the plant material, often leaving behind the characteristic irregular holes and silvery slime trails that indicate their feeding activity.
Conversely, slugs tend to avoid plants with strong aromatic oils, bitter compounds, or tough, rough, or hairy leaves, which make feeding difficult or unpalatable. Plants like lavender, rosemary, fennel, and many species of geraniums are often left untouched because their texture or chemical defenses deter the mollusks. Waiting to plant seedlings until they are more mature, with thicker leaves and a higher lignin content, can also help protect them from slug damage.
Utilizing Food for Trapping and Observation
The specific feeding preferences of slugs can be leveraged to attract them for monitoring or removal. Slugs are strongly drawn to the scent of fermentation, which is a reliable indicator of decaying organic matter and yeast. This biological attraction is the basis for using fermented liquids as lures.
A popular method involves using shallow containers baited with beer or a simple mixture of water, sugar, and baker’s yeast, which creates a strong fermenting odor. The yeast and volatile compounds, not the alcohol itself, are the primary attractants, drawing slugs from the surrounding area. Vegetable scraps, particularly melon rinds or a small amount of cornmeal, also serve as highly attractive temporary bait stations.
However, the odor of strong attractants like beer can also draw slugs from further away, potentially increasing the local population temporarily. For effective trapping, the bait must be placed in a container with deep, smooth sides to prevent the attracted slugs from crawling back out after they enter.