Slugs are one of the most destructive and difficult pests to control. Seedlings of many vegetables and flowers are favored foods, and high populations of slugs can cause difficulties in establishing a crop. Slugs also feed on many fruits and vegetables prior to harvest. This preharvest feeding results in wounds that allow various fungi and bacteria to enter and spoil the crop. In addition, the slime trails produced by slugs can contaminate garden produce.
Source: Colorado State University