Fruits and vegetables in direct contact with the soil are attacked more frequently than those off the ground. In Wisconsin, tomatoes often are attacked just as they ripen. Because they are primarily nocturnal feeders, slugs may not be visible during daytime examinations of damaged plants. A shiny trail of a sticky secretion may be associated with the damage, and is diagnostic of slug feeding. Many species of slugs are found in Wisconsin, and the most damaging are the gray and spotted garden slugs.
All northern species have similar habits and life cycles.
Both adults and eggs overwinter, and slugs become active during the warm days of early spring. Most feeding is done at night or during cloudy days. Slugs lay eggs in clusters in damp, shaded soil, and eggs hatch within 3 to 4 weeks. Slugs develop slowly and may live for over a year. Slugs cannot survive in direct sunlight, and need high humidities and cool temperatures to thrive.