Slugs and snails
Also known as Garden snail, Grey field slug, Giant African land snail, Lissachatina fulica
In short
Slugs and snails are molluscs that graze leaves, flowers, seedlings and soft fruit, mainly at night and in damp weather. Their smooth-edged holes and silvery slime trails give them away. In the tropics, the invasive giant African land snail is a major plant pest and can carry a parasite dangerous to people.
How it looks
Soft-bodied animals that glide on a muscular foot and leave a mucus trail; snails carry a coiled shell, slugs have no external shell. Garden slugs such as the grey field slug (Deroceras reticulatum) are a few centimetres long, grey to brown and mottled. The giant African land snail (Lissachatina fulica, formerly Achatina fulica), established in Malaysia since 1911 and across tropical Asia, is much larger, reaching about 7 cm across and 20 cm or more in length. All hide by day under pots, boards, leaf litter and dense groundcover, and feed at night or on cloudy, wet days.
Signs
Irregular holes with smooth edges in leaves and petals, seedlings grazed to stumps, soft fruit hollowed, and shiny silvery slime trails on leaves, pots and paths; droppings nearby.
Life cycle
Most are hermaphrodites and lay clusters of round, pearly white eggs in damp soil or under debris. The brown garden snail takes about two years to mature and may lay around 80 eggs up to six times a year; slugs mature faster, in about three to six months.
What favours it
Damp, shaded places with plenty of hiding spots; frequent evening watering; rainy seasons. Pots grouped on the ground give them cover.
Prevention
- Remove hiding places such as boards, weeds, dense groundcover and debris near plants.
- Water in the morning rather than the evening, and use drip irrigation where possible.
- Protect seedlings until they are sturdy; grow less palatable plants in exposed spots.
- Fit copper bands around pots or beds as a barrier.
Treatment
Start with the first step and move down only if the problem persists.
- Hand-pick at night by torchlight; wear gloves, and never handle giant African land snails with bare hands — they can carry rat lungworm (Angiostrongylus cantonensis), which can cause a life-threatening infection. Wash hands afterwards.
- Trap under boards or upturned pots and collect them in the morning.
- If needed, iron phosphate baits, scattered thinly on moist soil in the late afternoon, are the safer option around pets and children — follow the product label. Metaldehyde baits are highly toxic to dogs and should be avoided where pets can reach them.
Pros and cons
Cons
- Can destroy seedlings overnight.
- Giant African land snails can carry parasites harmful to people.
Look-alikes
- Caterpillars
- Leave dark frass pellets rather than slime trails.
- Earwigs
- Leave ragged holes in petals and leaves, with no slime; found hiding in tight crevices.
Affected plants
Seedlings, leafy vegetables, hostas, orchids and other soft-leaved plants, ripening strawberries and tomatoes; the giant African land snail eats a very wide range of crops and ornamentals.
Related
Sources
Written in our own words from these sources. Check a product label before using any treatment.