What Is a Narwhal Tusk? The Tooth That Grows Through the Lip

A tooth, not a horn

The narwhal is a toothed whale, but its mouth is strangely empty. Apart from a few tiny leftover teeth, it has just two teeth, both canines set in the upper jaw. In females both usually stay hidden inside the skull. In males, the left canine starts to push out through the upper lip when the whale is about two or three years old.

From then on the tooth keeps growing, straight forward from the left side of the head. It sticks out of the lip rather than out of the mouth, which is one reason it looks so much like a horn. Inside, it has the same basic layers as other teeth: a central pulp with nerves and blood vessels, surrounded by dentin, with a thin outer layer of cementum.

The tusk is hollow for much of its length and is lighter than it looks, yet still strong and somewhat flexible. Narwhal tusks can bend noticeably without snapping, which helps them survive knocks and clashes.

How long and heavy is a narwhal tusk?

Most male tusks measure about 1.5–3 m (5–10 ft) long, and a large one can weigh around 7–10 kg (15–22 lb). On a whale whose body is only 4–5.5 m (13–18 ft) long, that makes the tusk one of the largest teeth, relative to body size, of any living animal.

Tusk length grows faster than body length as a male gets bigger, so the largest, oldest males carry by far the longest tusks. Many tusks have broken tips, a sign of a hard life among ice and rivals.

Why does the tusk spiral?

Every narwhal tusk twists in a left-handed spiral, counterclockwise when seen from the base. The twist runs along the whole length and gives the tusk its famous candy-cane grooves.

Nobody knows exactly why it spirals. The tooth may rotate slightly as it grows, and studies of the tusk’s microscopic structure show layers of fibers wound in opposite directions, which may help the long tooth grow straight and resist bending. Even in the rare whales with two tusks, both usually twist in the same left-handed direction.

Do female narwhals have tusks? Double tusks

Most females have no visible tusk, but a minority grow one, usually shorter and less strongly spiraled than a male’s. Estimates of how common this is vary from study to study. Because tuskless females live as long as males and raise calves successfully, the tusk clearly is not essential for feeding or survival.

Very occasionally a male grows two tusks, when the right canine erupts as well. Double-tusked skulls are prized museum specimens, and a few females with two tusks have also been recorded.

What is the narwhal tusk used for?

Scientists have proposed many uses over the centuries, from breaking ice to spearing fish and digging in the seabed, but there is little evidence for most of them. Today the leading explanations are:

• A signal to females and rivals. Most researchers see the tusk as a product of sexual selection, like the antlers of a deer or the tail of a peacock. A 2020 study found that tusk length increases faster than body size, a typical pattern for ornaments used in mating competition.
• Ranking among males. Males often cross and rub their tusks above the surface, a behavior called tusking, which may help them size each other up without serious fights.
• Sensing the water. The tusk is full of tiny channels leading from the surface toward the nerves in the pulp, and researchers have estimated it has millions of nerve endings. A 2014 study reported that narwhals’ heart rates changed when the water around their tusks switched between seawater and fresh water, suggesting the tusk may sense differences in salt.
• Occasional feeding help. In 2016, drones filmed narwhals in Tremblay Sound, Nunavut, tapping Arctic cod with their tusks to stun them before eating them. This is probably an extra use, not the main purpose.

Compare this with walruses, whose tusks are also canine teeth but are carried by both sexes and used for hauling out on ice and fighting (see What are walrus tusks for?).

The tusk and the unicorn horn trade

For centuries, narwhal tusks were sold in Europe as the horns of unicorns. Traded south from Greenland and the Arctic, often without any description of the animal they came from, they were believed to detect and neutralize poison and were worth far more than their weight in gold. Kings and emperors displayed them in treasuries, and the Danish coronation throne was built partly from narwhal tusk.

In 1638, the Danish naturalist Ole Worm showed that so-called unicorn horns were really narwhal teeth, and belief in their magic slowly faded. Today the trade in narwhal tusks is controlled under international law, and Inuit hunters in Canada and Greenland may sell tusks from regulated hunts. For more on the legend, read Are narwhals real?, and to see where these whales live, see Where do narwhals live?