Their major natural predators are:
- FROGS. They require: ponds & steams with access. Low dense vegetation or cover to lay-up in during the day (they are mainly nocturnal). Their predators are: owls, seagulls, grass snakes, cats, crows, weasels, stoats, foxes, rats, hedgehogs, pike etc. They hibernate so must have: hole in the ground under tree or rocks, tree root, old log, stone wall, compost heap etc. In a very good hibernation location, frogs, newts, toads, lizards and snakes may overwinter together. Large frogs eat large slugs & snails; smaller eat smaller. They eat snail shells too. Slugs are a very high proportion of diet. They can live for 10 years.
- SONG THRUSHES, MISTLE THRUSHES AND REDWINGS. They require: Food: As well as slugs & snails which they eat all year, worms early in the year, caterpillars in summer, fruit & berries in Autumn & Winter. For nesting: dense hedges & bushes. Not too many predators: cats, magpies etc. It is believed their numbers have been greatly reduced by slug pellets & from competition with the greatly increased number of blackbirds.
- GROUND BEETLES. Energetic hunters of slugs and other creatures. Breed more slowly than slugs & can't keep up with sudden slug increases. They require Summer nesting sites: stones or logs etc. Many species are active for only a few weeks in Spring & Summer before entering a resting period before laying eggs in Autumn. Require cover while hunting: under plants, debris, mulches, etc. Most species prefer moist shady conditions & feed mainly at night. A few are active in the day & prefer more open ground. Require overwinter sites: under logs, tree bark, in the soil or in a patch of rough grass. Most tend to move to woodland or hedgerows in the Winter. In Spring & Summer, ground beetles eat many eggs & young slugs. To encourage beetles, it is possible to construct the following "Pitfall plot":
- HEDGEHOGS. They require: Cover, hedges, undisturbed leaves, or brushwood. No major roads nearby or solid wall protection. They eat large numbers of slugs and small snails, also beetles but on balance do more good than harm. They require hibernation sites: piles of leaves or brushwood or hibernation boxes under sheds etc.
- COMMON SHREW. They require: Cover, especially long rough grass. Undisturbed site for nest, especially a hole or burrow in the ground. Their predators are cats, owls, dogs, weasels & crows. Their diet consists of earthworms, beetles, spiders, woodlice & many slugs & snails.They remove the slime from slugs first. They hunt especially at dusk, night & dawn.
- PARASITIC NEMATODE. Phasmarhabditis hermaphrodita. Commercially available. See links page for suppliers. Should stop slugs feeding quickly. Slugs die within a week, underground. Sprays containing the nematode are effective for 6 weeks after spraying in wet or dry conditions and down to at least 5ºC. Nematodes do not like manure. Further generations emerge from the dead slug bodies. Apply before planting or sowing a valuable crop.
- MARSH FLIES. Tentancera elata & Eurthycera cribata. Parasites of snails & slugs. Each fly larva may kill 9 to 25 snails or slugs by burrowing. They require a wildlife pond & wild flowers.
- SLOW WORMS. They require: an undisturbed spot, a compost heap is ideal. Vegetation, a sunny spot: woodland clearing, old ivy covered wall, hedge bank, railway embankment, corrugated iron sheet laid on the ground etc. Eat especially small white slugs, also other slugs & some snails. They are more effective after rain. They can live 30 years.
- CENTIPEDES. They require darkness, moisture, protection by plants, debris, stones, etc. Wholely carnivorous> Eat insects, worms & many slugs & snails. They require not too much predator activity by hedgehogs & birds. Their main escape is their fast speed of movement.
- COMMON NEWT. They require: Pond without predatory fish, cover to lay up in the day time. A good spot to hibernate in: hole in the ground, under rocks etc. Not too many newt predators: see frog predators.
- BACILLUS THURUNGIENSIS. A bacteria which causes paralysis of insect gut muscles and subsequent death. Some strains parasitise slugs. May become commercially available. Easily sprayed on plants to infect slugs.
- OTHER PREDATORS OF SLUGS & SNAILS. -Though only a small part of their diet- include: rooks, jackdaws, jays, magpies, starlings, blackbirds (eat snails in winter), fieldfare, gulls, owls, robins, toads (they were once commonly kept in greenhouses to control slugs & snails), moles, common lizard, foxes, mice, rats, testacellid carnivorous slugs (identified by a small shell at hind end of body. They hunt underground. Are not very common) and glow worms (eat a few small snails).
Introduce domestic predators
- DUCKS. Especially Indian runner (which can't swallow frogs & toads, Harlequin, Kharki Campbell have proved successful. Types of duck which naturally have a low vegetable diet, or are natural mollusc feeders. They should at first be carefully observed to ensure they are eating slugs and snails and not damaging garden plants. Strawberries will need to be netted. They may be introduced into the garden only for short periods when there are slugs about, or given a very extensive range to forage in. They should be allowed access to their prefered green foods (if any) at all times; and not at the same time allowed to feed in deep water, where they will prefer to forage.
- HENS. Small breeds only. Large strong hens are very destructive - lumps of vegetation go flying. They can be trained to come when called to strategically placed pieces of carpet or wood, to eat hiding slugs & snails & woodlice. When confined, they will clear the ground of slugs & snails & of most vegetation! Maybe introduced into gardens for short periods or given very extensive range. Some plants such as soft fruit or lettuce must be protected.
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