Slugs, Snails & Freshwater Bivalves

As familiar gardeners’ pest, slugs and snails belong to a class of animals called Gastropoda, which also include the sea snails and slugs, as well as freshwater snails, bivalves and limpets. In turn this group fall under the classification phylum Mollusca, which are the molluscs and include octopus and squid, amongst many other species. The word Gastropod comes from the Greek language translating to “gastro” meaning stomach and “pod” meaning foot, referring to the animal’s foot being positioned below its guts.

There are around 46 species of terrestrial slug in Britain and Ireland, and about 120 species of land snail. The difference between slug and snail is initially obvious, as snails have a coiled shell made from calcium carbonate which they can retreat inside of when threatened or to avoid dessication in hot weather, where as slugs lack an outer shell. Slugs evolved from snails, reducing their shell to a plate which is found internally under the skin towards the tail end. Both slugs and snails are air-breathing, and have a lung within the mantle cavity, and in slugs can be seen a large breathing pore called the pneumostome which leads to the lung. They also have a large fleshy foot which helps them traverse their environment, and they produce mucus which helps them slide along, and can help with protection when attacked.

Slugs and Snails have voracious appetites, and this is why they are hated by gardeners and growers. They don’t solely feed on the leaves of live plants, but will also eat fruit and vegetables, some prefer decaying plant material or fungi, algae or lichen. Most species of slug will scavenge and feed on other dead or dying slugs and snails, whilst some will attack and kill worms with powerful blade-like teeth.


Large Red Slug (Arion (Arion) rufus)
Large Red Slug
Arion (Arion) rufus
Brown Soil Slug
Arion (Kobeltia) distinctus
Green Cellar Slug
Limacus maculatus
Netted Slug
Deroceras (Deroceras) reticulatum
Dusky Slug
Arion (Mesarion) subfuscus
Tree Slug
Lehmannia marginata
Iberian Threeband Slug
Ambigolimax valentianus
Chestnut Slug
Deroceras (Deroceras) invadens
Tawny Soil Slug
Arion (Kobeltia) owenii 
Leopard Slug
Limax maximus
Balkan Threeband Slug
Ambigolimax nyctelius


Garden Snail Cornu aspersum
Garden Snail
Cornu aspersum
Kentish Snail
Monacha (Monacha) cantiana
Glossy Glass Snail
Oxychilus (Oxychilus) navarricus
Two-toothed Door Snail
Clausilia (Clausilia) bidentata
Wandering Pond Snail  Radix balthica
Wandering Pond Snail
Ampullaceana balthica
White-lipped Snail Cepaea hortensis
White-lipped Snail
Cepaea (Cepaea) hortensis
Strawberry Snail (Trochulus striolatus)
Strawberry Snail
Trochulus (Trochulus) striolatus
Cellar Snail
Oxychilus (Oxychilus) cellarius
Common Chrysalis Snail Lauria cylindracea
Common Chrysalis Snail
Lauria (Lauria) cylindracea
Great Pond Snail Lymnaea stagnalis
Great Pond Snail
Lymnaea stagnalis
Brown-lipped Snail (Cepaea nemoralis)
Brown-lipped Snail
Cepaea (Cepaea) nemoralis
Shiny Glass Snail
Zonitoides (Zonitoides) nitidus
Discus Snail Discus rotundatus
Discus Snail
Discus (Gonyodiscus) rotundatus
River Snail
Viviparus viviparus
Pfeiffer's Amber Snail Oxyloma elegans
Pfeiffer’s Amber Snail
Oxyloma (Oxyloma) elegans

Freshwater Bivalves

Asian Clam
Corbicula fluminea
Swollen River Mussel
Unio (Unio) tumidus
Duck Mussel
Anodonta (Anodonta) anatina
Painter’s Mussel
Unio (Unio) pictorum

Many thanks to Ben Rowson and Chris du Feu from iRecord who helped confirm and correct species where appropriate.

Useful AIDGAP reference books:

Slugs of Britain and Ireland by Ben Rowson, James Turner, Roy Anderson and Bill Symondson.
Land Snails in the British Isles by Robert Cameron.
Freshwater Bivalves of Britain and Ireland by Ian Killeen, David Aldridge and Graham Oliver.