Why Do Cobras Spread Their Hoods? How the Cobra Hood Works

How does a cobra’s hood work?

The hood is built from the snake’s own skeleton. A snake’s ribs run along most of its body, and in cobras the ribs just behind the head, in the neck region, are unusually long, flattened and mobile. When the cobra is at ease, these ribs lie folded back along the body and the neck looks ordinary.

When the snake is alarmed, a set of muscles attached to these ribs contracts and pulls them outward and forward. The loose neck skin between them is stretched tight, rather like the fabric of an umbrella being opened. Studies of cobra anatomy have identified several neck muscles that work together to raise and spread the ribs; the hood is an active display, not something that simply inflates.

The width and shape of the hood depend on the species. Indian and monocled cobras have broad, rounded hoods. The king cobra, which is not a true cobra of the genus Naja, has a narrower, longer hood.

Why spread a hood at all?

Cobras have potent venom, but a fight is risky even for a venomous snake: it can be injured, and venom takes time and energy to replace. A display that scares a threat away without biting is cheaper and safer. Biologists call this kind of signal a warning display.

The hood helps in several ways. It makes the snake look bigger from the front, so a predator may judge it too large or dangerous to tackle. It also raises the head and shows off any markings. Combined with the snake rearing up and hissing, the effect is hard to miss.

Most of the animals cobras want to deter are predators, such as mongooses, birds of prey and large mammals that might step on them. People are treated the same way.

Rearing up: the rest of the display

A hooding cobra usually lifts the front part of its body off the ground at the same time. Studies of captive cobras found that they raised about 13–22% of their body length while hooding. A large king cobra, which is usually 3.2–4 m (10.4–13.1 ft) long, can lift its head a meter (3.3 ft) or more off the ground and can even glide forward in this pose.

Rearing up brings the snake’s eyes level with a threat and lets it strike downward or forward. It also makes the snake easier to see. Cobras often sway slightly from side to side to keep their eyes on a moving threat, which is the movement snake charmers exploit. Our article can snakes hear? explains why charmed cobras follow the flute, not the music.

What do hood markings mean?

Many cobras have bold patterns on the back of the hood that are only fully visible when it is spread.

The eye-like markings may act as false eyes, making a predator approaching from behind think the snake is watching it. This idea is widely repeated, but it has not been tested thoroughly. Dark throat bands on the front of the hood may make the display more conspicuous from the front.

Hissing, spitting and the king cobra’s growl

Most hooding cobras also hiss by forcing air out of the lungs. The king cobra makes an unusually low-pitched hiss, often called a growl. Its sound lies below 2,500 Hz, with a dominant frequency near 600 Hz, while most snake hisses span roughly 3,000–13,000 Hz. Small pouches off the windpipe act as resonating chambers and deepen the sound. The Oriental rat snake, one of the king cobra’s prey, has similar pouches and can also growl.

Some cobras add another weapon. Spitting cobras of Africa and Asia can spray venom from small forward-facing openings in their fangs toward the eyes of a threat, often while hooded. The rinkhals of southern Africa can spit too, and it is also known for playing dead. Venom in the eyes is a medical emergency; anyone affected should seek emergency medical help immediately.

Other snakes that hood

Hooding is best developed in cobras, but it is not unique to them. The rinkhals, some Australian elapids, Asian keelbacks and North American hognose snakes all flatten or spread their necks when threatened. In the harmless hognose snakes, the display is a bluff: they spread a cobra-like neck and hiss loudly, and if that fails they may roll over and play dead.

Other reptiles use similar tricks to look bigger, such as the bearded dragon, which spreads its spiny throat. See why do bearded dragons puff up?

What to do if you see a hooded cobra

A cobra with its hood spread is alarmed, not hunting. The best response is to stop, step back slowly and give it plenty of space so it can escape. Never try to touch, catch or corner a cobra. If anyone is bitten, seek emergency medical help immediately by calling the local emergency number, such as 112 in many countries.