Dog whelks are inter-tidal snails with a shell which is conical with a rounded spire. The shell is usually white, grey or cream-coloured, though size, shell thickness and colour vary. It is distinguished from other seashore shells snails by the distinct groove along the shell lip and is slightly smaller than the common whelk. The animal itself, which is rarely seen, is white or cream coloured with white speckles and a flattened head which bears two tentacles, each with an eye.

Behaviour

Dog whelks have specialised ‘tools’ to target their favourite food, mussels and barnacles. A modified radula (a toothed chitinous structure) is used to bore a hole in the shells of prey, complemented by an organ on the foot which secretes a shell-softening chemical. When a hole has been formed, (which can take many hours), paralysing chemicals and digestive enzymes are secreted inside the shell to break the soft body down into a ‘soup’ which can then be sucked out with an extensible proboscis.

The sexes of the dog whelk are separate, with full maturity attained at around three years. They reproduce by aggregating, (thirty or more individuals), for the mating season in the spring. Spawning is protracted, and ends in autumn. The number of eggs per female ranges between 100 and 1000; they are laid in April/May in protective yellow capsules in suitable crevices or under rock overhangs on the shore. The young feed on unfertilised eggs before emerging from the egg capsules as almost fully formed, but very small replicas of adults.

Size

• Length: 2-3cm (up to 6cm)
• Lifespan: 5-10 years

Status

Not under threat.

Dog whelk numbers were decimated in the 1970’s as a side effect of tributyltin (TBT) – a highly toxic chemical found in antifouling paint used on boats. Research revealed that female dog whelks began to develop male sex organs when exposed to even minute levels of TBT. Females were unable to release their eggs for fertilisation. The use of TBT gradually became restricted with an international ban coming into force in September 2008.

Distribution

This species is found around the coasts of Europe and in the Northern West Atlantic coast of North America. It can also be found in estuarine waters along the Atlantic coasts. Dog whelks are abundant throughout rocky coastlines around the British Isles.

When to see

January to December

Facts

• In medieval times, the dog whelk was used to acquire beautiful red, violet and purple dyes. The dye came from mucus in a gland known as the hypo-branchial gland. This chemical substance passes from yellow to green and then to blue, reds and purples when exposed to air and sunlight.
• The dog whelk can only survive out of water for a limited period. It will gradually become desiccated and the organism can no longer function properly. Furthermore, the dog whelk has to excrete its toxic waste directly into water. It has no adaptation to produce uric acid for excretion of ammonia.