The following facts I found in my documents, (using nematodes-without my judging!):
Infestations are less serious in dry weather but tend to become a problem during prolonged rainy weather. An individual grey field slug has the potential to produce 90,000 grandchildren and has approximately 27,000 teeth!
They live underground during the day, emerging at night to feed. One cubic metre of garden will on average contain up to 200 slugs. Slugs eat leaves, stems and roots of plants, weakening them and often causing them to die. They leave slimy trails over plants and soil, and are particularly devastating to seedlings and cuttings. Slugs leave their own individual scent trails so they can find their way home. Use packs of microscopic beneficial nematodes (eel worms) which are watered into pots or open ground with a watering can or hose. They enter the slug through a hole in its back while it is underground and poison it so that it will die within a few days underground, out of sight. Nematodes can be used indoors or outdoors, when temperatures are above 5°C. They remain in sufficient concentration to give good effectiveness for about 6 weeks. The best time to kill slugs is when the young are hatching in the spring, but nematodes can be applied all year round, whenever slugs are around. This year we were applying them in our glasshouses in January! Nematodes travel by slithering around the soil particles so the soil needs to be kept moist. If it is hot and dry they will either shrivel and die or hide away deep underground. These nematodes will kill snails if they come into contact with the soft part of their body. However snails feed on the surface, and the nematodes usually work underground within the soil so they are not a foolproof way of controlling snail populations. (The best way to deal with snails is to pick them off by hand or use a slug and snail trap).
"To know what we know, and know what we do not know, that is understanding."(Confucius) Eco Thai German Farm, farmersvoice