Slugs and snails are probably the number one pest, with no garden ever completely free from them. They are mainly nocturnal feeders and overnight can completely destroy rows of seedlings or wreak havoc on established plants such as dahlias.

 

Both slugs and snails tend to produce elongated rather than round holes. They leave a trail of slime, which is secreted as an aid to movement. The presence of this clear shiny material together with the shape of the holes is a sure sign that slugs or snails are responsible for the damage.

 

Slugs and snails are molluscs, and the main difference between them is that slugs have lost their outer shell, relying on a small internal shell under the skin of their back as their sole protection.

 

The eggs, which are translucent through to cream, depending upon the species, can be up to 2cm/1⁄10in in diameter. They are fused to form a sphere up to 1cm/½in in diameter and are hidden under stones or pieces of wood.

 

The eggs hatch in the spring to produce young that are perfect miniatures of the adult form. They will take a full season to mature. Slugs overwinter by burrowing into the soil, but snails retract into their shells and develop a covering over the soft, exposed parts.

 

They do not hibernate, and providing the temperature is above freezing they will feed all the year round. However, it is during the moist, humid time following a heavy shower of rain that they are most active and do the greatest amount of damage.

 

There are many different species of slugs. Some are quite small, and it is these which often do the most damage.

 

• The commonest is the garden slug. These vary from shiny black to pale grey and are usually less than 4cm/1½ in in length.

• The larger, so-called black slug is not always black, but can be reddish brown or yellowish. The adults can reach 20cm/8in in length.

• Another common species is the field slug, which is mainly grey-brown, and less than 4cm/1½in in length. Like the garden slug, it occurs in large numbers.

• The main snail pest is the garden snail, which as the name implies has readily adapted to garden conditions. At 4cm/1½in, these brown and grey shelled specimens are among the largest of the British snails.

• The banded snail is a smaller species, and quite attractive in appearance.

 

But although they are often thought of as doing much less damage, these voracious vegetarians can quite quickly destroy both seedlings and established plants.

 

Prevention

 

Young slugs prefer to feed on decaying organic matter before progressing to living plants.

 

• Make the area less attractive by only using fully rotted manures or composts.

• Practise good garden hygiene – clear away dead leaves or anything lying around that can provide shady refuge during the day.

• Do not allow stones, wood and other material to rest against walls where they will provide hiding places.

• Do not allow weeds to remain in the ground as these will also provide cover for the travelling molluscs.

• As soon as crops are over, pull up all dead and decaying material and place on the compost heap.

• Cultivation of dry ground in the summer will desiccate any burried slugs.

• Cleared ground may also reveal large numbers of slugs, which should be collected and disposed of.

• The chemical treatment is to scatter slug pellets around seedlings and tender shoots.

 

• Cover the pellets with pieces of ceramic material to protect them from the rain.

• Make sure that the pellets cannot be picked up by pets.

• An alternative is to use an aluminium sulphate-based slug killer, which is only harmful to slugs and snails, not higher animals. Alternatively a biological control using special nematodes is available.

 

Non-chemical methods are seldom capable of destroying the pests faster than they can be replaced and are only effective in those areas where slugs and snails are not a major problem.

 

• A ring of sharp sand, ash, crushed eggshells or lime around the plants all afford some protection as the molluscs have sensitive skins and are reluctant to expose their bodies to these substances.

• Beer traps are sometimes recommended, but very few slugs will be caught compared to the numbers in the immediate area.

• In addition, beneficial creatures are also as likely to be caught in the trap (such as earthworms, harvestmen, spiders, centipedes, ground beetles).