Slugs are the number one plant pest problem, they are usually, but not exclusively herbivores. Slugs are hermaphrodite and lay spherical translucent white eggs about 2-3mm across. Eggs are laid in batches of 10-50 and can often be found in the soil, in compost heaps and other dark, damp places. Up to about 500 eggs per slug may be laid in a season. Slugs can live for up to four years but the lifespan is usually less. Slugs are soft bodied, gastropod molluscs that move along on a singular muscular foot and secrete slime. They have two sets of retractable tentacles, one pair for smell and taste and one pair for eyes. They scrape their food up with a spiky, rasping tongue. Slugs can be active all year round both above and below ground in all but very hot, dry or frosty weather. Slugs mostly feed at night. They attack young and tender garden plants, especially annuals, perennials and vegetables, Slug damage is most severe during humid periods, especially in Spring and Autumn. Slugs are more mobile in wet weather because their slime is hygroscopic; it draws in moisture. Slime becomes far more effective in wet conditions. It’s this hygroscopic property that makes slug slime so hard to wash off your hands. Adding water just makes it more slimy!
The most common species of slug found in gardens and allotments :-
Spanish slug
6-15cm, when mature, chocolate brown with dark brown tentacles.
Balkan Threeband slug
4-8cm, when mature, greyish brown, often found in compost bins, under logs or plant pots.
Large Red slug
6-15cm, when mature, grey with bright orange foot fringe.
How to control them?
Barrier methods are more environmentally friendly, slugs do not like crawling over a rough surface. Crushed egg and nut shells, horticultural grit, coffee grounds, sawdust, sandpaper or pine needles placed around plants make it more uncomfortable for the slugs to cross. Cheap but needs replenishing frequently. Copper tape around pots – slugs experience a small shock when exposed to copper, which will make them turn back. Beer trap – use a shallow container (plastic coleslaw or yoghurt pot) and insert it into the soil. Leave a rim 2cm above soil level to prevent beetles and other creatures from falling in.
Organic control – There is a microscopic nematode Phasmarhabditis hermaphrodita which kills slugs. It is a native species and can be found naturally in the soil throughout the UK. For it to be effective, however, you need large numbers and regular application. The nematodes are commercially available, often supplied in a pack of moist clay. This is mixed with water and applied to the soil with a watering can. Slugs will be controlled for up to 6 weeks, after which reapplication is often necessary. Expensive and mail order only.
Chemical methods – slug pellets, when scattered around plants, these are eaten by the slug and they burrow into the ground and die. Two types available, standard, based on metaldehyde or methiocarb and organic, based on ferric phosphate, these are pet and child friendly. Cheap, but expect to pay more for organic pellets, readily available.
Natural predators, slugs have a variety of predators such as:
Hedgehogs, Birds (e.g. Thrushes), Toads & Ground Beetles
When a slug is attacked by a predator it will contract its body to make it a smaller target. The mucus that covers a slug’s body doesn’t taste very nice and is slippery, so this is why you will often see birds wiping slugs on the grass before they eat them.