WHILST snails and slugs are often the bane of gardeners and horticulturalists alike due to their propensity for feeding on crops and ornamental plants, and are considered as pests, it should be remembered that not all species cause damage and they are also an important food source for a number of natural predators. Controlling slugs and snails in your garden can have a severe impact on this important food source for other animals such as hedgehogs and birds such as the song thrush whose numbers are already threatened by many other habitat, climate and human challenges.
In the UK there are approximately 100 species of land snail and approximately 40 species of slug. Land snails and slugs are molluscs and gastropods- gastropod literally means an “eating foot”. All land slugs have evolved from land snails with the most obvious visual difference being the lack of a shell although slugs still have the remnants of a shell, known as a “vestigial shell”.
This vestigial shell is found externally in a small number of UK species, however in the majority it is now located internally. They have nearly 30,000 teeth and both secrete mucus which helps them glide over a surface; this slimy mucus also acts as a deterrent to would be predators.
A bird can sometimes be observed to wipe away this mucus on grass and plants prior to ingestion. Land snails have no hearing organs but have both sight and olfactory (smell) organs. It is their good sense of smell that helps them find food.
Snail shells essentially consist of calcium carbonate. Snails are born with colourless soft cells known as a “protoconch” and they need to consume a lot of calcium to help the shell to harden. The shell continues to grow as the snail grows; the number of whorls or spirals in the shell increases and the protoconch ends up in the centre of the spiral of the snails shell. Similar to tree rings these rings can be used to estimate the age of the snail.
Most snails are hermaphrodites, meaning that they have both male and female reproductive organs but mate with a partner as they do not fertilize their own eggs. Following mating both snails lay eggs thus increasing the overall chances of survival. The resulting eggs are tiny and are dropped into moist soil and take up to four weeks for to hatch.
One of the most common species encountered in our gardens is the garden (common) snail, Cornu aspersa. The body is greyish and the adult shells are 25–40 mm in diameter and 25–35 mm high, brown in colour with darker brown markings with a white lip. They have two long tentacles, each with an eye at the tip. Below these eye stalks are two shorter tentacles which help the snail to feel where it is going. The mouth is situated between these two lower tentacles. They are primarily herbivores feeding on vegetable crops, cereals, fruit trees and garden flowers, but will scavenge on rotting plant material and occasionally on animal matter, such as crushed snails and worms.
In late autumn they start to search out places in which to hibernate where they will often form large groups in tree crevices and under rocks and stones. Once a secure place has been found they seal themselves into their shells.