Why Do Atlas Moth Wings Look Like Snake Heads? Mimicry Explained

What do the snake-head wingtips look like?

The Atlas moth is one of the largest moths in the world, with a wingspan of about 24–28 cm (9.5–11 in). Each forewing ends in a broad, hooked extension. On this tip, edged in yellowish tones, a dark spot sits where a snake’s eye would be, and darker lines add to the effect. The curved outline looks like the head and neck of a snake viewed from the side.

When the moth rests with its wings spread, the two forewing tips point outward like a pair of snakes rising from either side of the body. The resemblance is strong enough that the moth is known in Cantonese as the “snake’s head moth”. To human eyes, some people see cobras, while others simply see a reptile-like head.

How does the display work?

Adult Atlas moths cannot feed and fly slowly, so they cannot easily escape a hungry bird by flying away. They spend the day resting, often in plain view on tree trunks, branches or leaves.

If a predator disturbs the moth, it may not fly at all. Instead it can drop to the ground and lie with its wings partly folded, then flap or shake them slowly. This movement makes the forewing tips sway and twitch like moving snake heads. A predator that hesitates, even for a moment, may give the moth the chance to survive.

This kind of behavior is called a startle display or deimatic display. The aim is not to look poisonous, but to surprise or frighten an attacker long enough to break off the attack.

How strong is the evidence?

The snake-head idea is widely repeated in books, museum displays and nature programs, and it is plausible. Many birds and lizards are cautious around snakes, and the wingtip markings match the shape and position of a snake’s head surprisingly well.

However, there appear to be few or no controlled experiments that test how wild predators actually respond to Atlas moth wingtips. Most of what we know comes from descriptions of the moth’s behavior and from comparisons with other insects. Scientists therefore describe snake-head mimicry in the Atlas moth as a reasonable hypothesis rather than a proven fact.

Some researchers also point out that the wingtips may work in more than one way. Large, contrasting markings can be startling simply because they are bold and unexpected, whether or not a predator “sees” a snake. Hiding the body shape among patterns and clear wing windows may also make the moth harder to recognize as food.

Eyespots and other moth defenses

Many moths and butterflies use their wings to bluff predators, and some have been tested experimentally.

• Eyespots. Large, round spots that look like eyes appear on the wings of many moths, including the European eyed hawk-moth and the North American Io moth, which hide their eyespots at rest and flash them when disturbed.
• Tested startle displays. In experiments in Sweden, peacock butterflies with intact eyespots were far more likely to survive attacks by blue tits than butterflies whose eyespots had been painted over.
• Conspicuousness. Experiments with artificial moth-like targets have suggested that bold, high-contrast spots can scare birds even when they do not closely resemble eyes, so being conspicuous may matter as much as eye-likeness.
• Camouflage. Many moths look like bark, lichen, dead leaves or bird droppings, avoiding detection in the first place. Stick insects use similar tricks, described in how stick insects hide.

Snake-mimicking caterpillars

Some of the most convincing snake mimics are caterpillars rather than adult moths. Several hawk moth caterpillars can swell the front of the body to reveal large eyespots that make them look like small snakes. The elephant hawk-moth caterpillar of Europe is one example. In the tropics of Central and South America, caterpillars of the genus Hemeroplanes go further: when disturbed, they turn over and inflate the front of the body into a convincing snake-like head, complete with “eyes” and “scales”.

The swallowtail butterflies offer another example. The spicebush swallowtail caterpillar of eastern North America has two large false eyes on its swollen front end, and the caterpillar of many swallowtail species can also push out a forked, smelly organ called an osmeterium when threatened.

Does the Atlas moth have other defenses?

Besides its wingtips, the Atlas moth relies on its large size, which may make it look like an unlikely meal, and on its ability to stay still for hours. The clear, triangular “windows” in its wings break up its outline. The caterpillars are covered in fleshy, waxy spines and are well camouflaged among leaves.

None of these defenses is perfect, and Atlas moths are still eaten by birds, lizards and other animals. But with adults that live only one to two weeks, even a short pause by a predator may give a moth time to mate and lay eggs. To see how big these moths really are, read what is the largest moth in the world?.