Check the boards each morning and destroy slugs found there. Another nonchemical control is placing 4-inch wide strips of fly screen on edge and partially embedded in the soil to keep slugs out of an area. Tall, dense stands of plants provide attractive conditions for slugs. Keep areas where they become a control problem thinned out sufficiently to allow for sunlight, air movement and good drying conditions. Natural predators of the slug include several species of ground beetle and fireflies, or lightening bugs.
Toads are their most important natural enemy.
Slugs will avoid crawling over anything dry, dusty or scratchy, such as lime, road dust, cinders, gravel or sand. The excessive secretion of mucus needed to free themselves from these materials soon exhausts them and they die. A border of any one of these inert materials will prove helpful in control. Other materials reported as helpful are 7 percent copper dust, hydrated lime and urea. Metaldehyde has worked well as a slug control chemical.