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Few animals inspire such fascination and intrigue as the Arctic-dwelling narwhal – discoveries of their long spiral tusk inspired legends about unicorns. But the true nature of the tusk is no less extraordinary, as Brett Westwood discovers in Radio 4’s Natural Histories.

1. Corpse whale

The term “narwhal” is Scandinavian and means “corpse whale”, which refers to the creature’s mottle grey-black skin colour – the colour of a corpse. In fact when they are born, the skin is pinkish – the mottling develops with age, becoming increasingly pale after four years. So the colouring can be used to give a rough estimate of how old a narwhal is.

Some narwhals live up to 100 years, but most live up to around 60 years.

2. Not a horn but a tooth

The most extraordinary feature of the narwhal is the long, spiral tusk which always has a left- handed spiral. No one is sure why it twists this way.

The tusk, which measures up to 3m in length, is actually a canine tooth which emerges from the left side of the upper jaw, through the lip.

Each male has a tusk, and occasionally two tusks, but fewer than 15% of females have one.

3. An engineering marvel

The narwhal tusk is a marvel of engineering. It is both very strong and very flexible – which is unusual – because if materials are very strong they are not usually flexible.

Unlike our own teeth, the narwhal tusk is soft on the outside and gradually gets hard and dense on the inside.

4. The narwhal and the unicorn

It’s thought that narwhals could be the origin of the unicorn myth. The great spiralling tusks of the narwhal, which were believed to be the horns of unicorns, were safeguarded in Churches from London to Kraków. The horns were treasured for their purifying and health-giving properties; cups made from the horns were claimed to be able to purify water and detect poisonous substances.

5. To joust or not to joust

The function of the narwhal tusk is still a hotly-debated subject. Many researchers believe it is used for sexual seduction, much like antlers on a deer. Females will typically mate with the males with larger tusks.

Other theories suggest the tusk is a sensory organ able to detect changes in the environment; an aid to navigation in pack ice; a weapon for doing battle with other narwhals and predators, and for hunting prey.

6. Stun gun

Narwhals feed primarily on Arctic cod, squid and Greenland halibut. In 2017, drone footage suggested that they can use their tusk to hit and stun fish near the surface.