How Do Stick Insects Hide? Camouflage, Swaying and Playing Dead

Looking like a twig or a leaf

The basic trick of a stick insect is to be mistaken for something inedible. Biologists call this masquerade: a predator may see the insect clearly but take it for a twig, a leaf or a thorn. The order’s scientific name, Phasmatodea, comes from the Greek phasma, meaning phantom.

The northern walkingstick of North America is a good example. Its body is a smooth brown or grayish cylinder, its legs are long and thin, and at rest it stretches its front legs straight forward beside the antennae. That hides the head and turns the whole insect into one long, forked stick.

Other phasmids copy different parts of plants:

• Leaf insects (family Phylliidae) of Southeast Asia and Australasia are flat and green, with leg flaps and body ridges that look like leaf veins, and even brown patches that look like bite marks or decay.
• Bark and moss mimics in tropical forests have knobbly bodies covered in outgrowths that resemble lichen or moss.
• Spiny species such as the giant prickly stick insect of Australia look like a bundle of dead, curled leaves.

Body shape is only part of it. Many species also have colors that vary between individuals, from green to brown, gray or reddish, which helps different insects match different backgrounds.

Keeping still and moving at night

A perfect disguise fails if the insect moves at the wrong moment, because birds and lizards spot motion quickly. Most stick insects therefore rest almost motionless through the day and do their feeding after dark. The northern walkingstick, for example, feeds most actively between about 9 pm and 3 am.

When they must move by day, many walk with slow, jerky steps, rocking back and forth as they go. Their position helps too. They often rest along a stem or leaf edge so that their outline continues the line of the plant.

Why stick insects sway

Many stick insects rock or sway from side to side, especially when a breeze blows or when they are disturbed. Studies of the giant prickly stick insect (Extatosoma tiaratum) found that its swaying has a rhythm similar to foliage moving in the wind.

Scientists think this helps in two ways. A swaying insect blends in with the movement of the leaves around it, so it is harder to detect. And if a predator does notice it, the motion makes it look even more like a plant, not an animal. Swaying is one of the clearest examples of camouflage that depends on behavior, not just appearance.

Changing color to match the background

Some stick insects can slowly adjust their color. The Indian stick insect (Carausius morosus) can become darker or lighter over hours, partly in a daily rhythm, by moving pigment in its skin cells. Several species also change shade from one molt to the next as they grow.

The small Timema walkingsticks of California go further: different populations have green, striped or dark forms, and each form tends to match the leaves or bark of its host plant. Experiments with Timema cristinae showed that birds remove more of the poorly matched insects.

Plan B: dropping and playing dead

If camouflage fails and a predator touches it, a stick insect has several backup tricks. The most common is to let go and fall into the leaf litter below, where it is hard to find again.

Many species also go rigid and motionless, often with the legs pressed along the body. This state, called catalepsy or thanatosis, is a form of playing dead. A stiff, lifeless insect looks even more like a fallen twig, and some predators lose interest in prey that does not move. It is a similar idea to an opossum’s famous act, described in why do opossums play dead?.

A stick insect seized by a leg can also break that leg off at a built-in weak point and escape. This is called autotomy. Young nymphs can partly regrow a lost leg over their next molts.

Startle displays, spines and chemical sprays

Some stick insects have bolder defenses, used only after they have been found:

• Flash colors. Winged species may suddenly open wings that are bright red, pink, blue or yellow underneath, sometimes while making a rustling sound. The surprise can make a bird hesitate. This is the same startle idea seen in moths, described in why Atlas moths look like snakes.
• Spines. Heavy species such as the jungle nymph (Heteropteryx dilatata) of Malaysia have spiny hind legs that they snap together like a trap, which can draw blood from a predator.
• Chemical sprays. Many phasmids have a pair of glands near the front of the thorax. The two-striped walkingstick (Anisomorpha buprestoides) of the southeastern United States can spray a strong-smelling fluid toward the eyes of an attacker. It contains a compound named anisomorphal, studied by the chemical ecologists Thomas Eisner and Jerrold Meinwald.
• Bad taste. Some species release distasteful blood from leg joints or bring up their stomach contents when grabbed.

The northern walkingstick relies almost entirely on camouflage and does not spray. If you meet a spraying species, simply watch it without handling. If spray reaches someone’s eyes and causes pain or vision problems, seek emergency medical help immediately or call 911 (US), 112 (EU) or 999 (UK).

Hiding starts with the egg

Camouflage begins before hatching. Stick insect eggs are hard capsules that look remarkably like plant seeds, and in many species they carry a fatty knob that tempts ants to carry them underground, out of reach of many predators and parasites. Newly hatched nymphs of some species even look and run like ants for their first days. Read more in how do stick insects lay eggs?.