Slugs are terrestrial mollusks, closely related to snails, but they lack the protective external shell needed to retain moisture. These soft-bodied gastropods are highly dependent on a damp, cool microclimate, which dictates where they live and feed. Understanding their food sources, environmental needs, and preferred hiding spots is the most practical step in managing their populations.
Primary Food Sources
Slugs possess a rasping organ called a radula, which they use to scrape and chew their food, allowing them to consume a highly varied diet. They are strongly attracted to tender, young plant growth, which is why seedlings, new shoots, and soft-leaved vegetables like lettuce and basil are often the first to show damage. Their feeding leaves behind characteristic irregular holes with smooth edges on leaves and can quickly decimate vulnerable new transplants.
The slug diet extends far beyond living plants, as they are essential decomposers in the ecosystem. They actively seek out decaying organic matter, such as fallen leaves, rotting wood, and other decomposing plant material, contributing to nutrient cycling. Slugs also feed on fungi and will opportunistically consume pet food left outdoors, carrion, and even other slugs.
One of the most powerful attractants is the smell of fermentation, which is often used deliberately in trapping methods. The yeasty aroma produced by beer or a simple mixture of water, sugar, and yeast draws slugs from a distance, highlighting their strong preference for fermented carbohydrates.
Essential Environmental Conditions
A slug’s physiology makes it extremely vulnerable to desiccation because its soft body tissue is composed mostly of water. Slugs must maintain contact with a highly humid environment to prevent fatal water loss, especially through the mucus they secrete for locomotion. They are generally active above ground only when the relative humidity is near 100%.
Slugs are most active during the night, cloudy days, or after irrigation, as sunlight and dry air force them into hiding. Their optimal temperature for activity is approximately 17°C (62°F), and they become relatively inactive when temperatures drop below 5°C or rise above 20°C. Practices such as overhead watering or having poorly drained soil create the necessary saturated conditions that allow slugs to move and feed freely without the risk of drying out.
Ideal Shelter and Hiding Places
When the sun rises or the air becomes too dry, slugs seek out specific physical structures that serve as cool, dark havens. These refugia provide protection from heat and predators while retaining the high level of moisture they require to survive the day. Removing these physical structures is often a successful method of population control.
Slugs frequently congregate under objects that create a tight, moist seal with the soil, such as low-lying boards, flat stones, and overturned pots. Dense ground cover plants and weedy areas also function as excellent daytime shelters by shading the soil and holding dampness close to the surface. Heavy layers of organic mulch, including straw and leaf litter, are particularly attractive because they offer an insulating blanket that keeps the underlying soil moist and cool.