You can tell if slugs have been picnicking when holes appear in foliage and the stems may be stripped of leaves. The sure sign is a silvery slime trail on leaves, the soil surface or paved areas of your garden. Slugs feed mainly at night, and after rain. They hole up underground or in damp garden litter during the day. This may be because their reproductive stage is so complicated that it must take all their time.
Slugs are hermaphroditic, each having both male and female reproductive organs.
Courtship involves circular slime trails and a kind of bungee jumping exercise where they climb trees then lunge downward on cords of slime. They both lay eggs in a damp spot among roots or under a rock, and the eggs hatch into sluglets in about a month. There's a horror movie in here someplace. Hata says that unfortunately, your best bet is to go out at night with a flashlight. With a trowel, scoop them off the plant and into a zip-lock plastic bag.