Do Grass Snakes Play Dead? The Death-Feigning Defense

What does a grass snake do when it plays dead?

The display usually happens after other defenses have failed, often when a snake has been picked up or pinned down by a predator. The snake writhes, then suddenly collapses and performs a sequence like this:

1. It goes completely limp, often twisting the body so that the pale, checkered belly faces up.
2. It opens its mouth wide and lets the tongue loll out, as if the snake had died with its jaws open.
3. It releases musk from glands near the tail, and may also empty its gut, so the snake smells like something rotting.
4. It may bleed from the mouth. Some snakes release a small amount of blood from the mouth or nose, called autohemorrhage.

If the snake is turned the right way up, it often flips over onto its back again, a sign that the act is deliberate. Once the danger seems to have passed, it slowly lifts its head, checks its surroundings and slides away.

Both the grass snake (Natrix natrix) and its western relative, the barred grass snake (Natrix helvetica) of Britain and western Europe, behave this way. The photo above shows a barred grass snake in southern France.

What other defenses come first?

Playing dead is the last resort in a whole series of bluffs. Grass snakes are shy, and most simply flee into water or vegetation as soon as they feel footsteps. If escape is impossible, they try to look dangerous:

• Flattening and puffing up the body and neck to look bigger.
• Raising the front of the body and flattening the head and neck, a pose often compared to a cobra.
• Loud hissing, produced by forcing air out of the lungs.
• False strikes, quick lunges toward the attacker, usually with the mouth closed. Real bites are very rare and harmless to people.

If the snake is grabbed, it writhes and coats its attacker with musk. Many grass snakes also regurgitate their last meal, which lightens them for escape and adds to the unpleasant smell. Only then does the snake usually turn to playing dead.

The musk comes from paired glands near the base of the tail. Its strong, garlic-like smell clings to skin, fur, feathers and clothing, and anyone who has handled a grass snake tends to remember it. It is not dangerous, but it is very unpleasant, which is exactly the point: a predator with a mouthful of foul-smelling snake may decide the meal is not worth it.

Why does playing dead work?

Death-feigning works because many predators react to movement. A heron, buzzard, fox or cat that grabs a struggling snake is triggered to keep attacking, but a limp, motionless prey can lose its interest. Some predators also avoid animals that already seem dead, since carrion may be diseased or spoiled.

The smell adds to the effect. A snake that looks dead, smells rotten and may have blood around the mouth is a very unappealing meal, especially for predators that prefer fresh, live prey. Even a moment of hesitation can give the snake its chance: if a predator loosens its grip or turns away, the snake can flee.

Scientists have studied the behavior in detail in North American hognose snakes, where the act is very similar, but the basic idea applies to grass snakes too: it costs little, and it does not need to work every time to be worthwhile.

Is playing dead unique to grass snakes?

No, but grass snakes are among its best-known performers. Similar death-feigning is known in:

Among European snakes, the venomous adder does not normally play dead; it relies more on its warning zigzag pattern and on biting. See the common European adder and snakes in the UK for how to tell the species apart.

Is it harmful to the snake?

The display itself does not harm the snake, but it is a sign of serious stress. Grass snakes are protected in many European countries and should not be picked up or disturbed. If you find one lying on its back in a garden or on a path, the kindest thing is to step back and leave it alone; it will usually recover and disappear within minutes.

People who find a “dead” grass snake sometimes discover later that it has vanished. It was probably never dead at all.