Slugs and snails are most active after dark or in wet weather, and the tell-tale slime trails can give you an indication of the level of activity in your garden.
Another sign that slugs and snails are in your garden is the distinct holes they leave in their wake. These pests make irregular holes in plant tissues with their rasping mouthparts. Young shoots and leaves are damaged or eaten, not only at ground level but often high up.
Luckily, these pests are easy to spot compared to other garden pests due to their size.