walking stick

walking stick, (order Phasmatodea, or Phasmida), any of about 3,000 species of slow-moving insects that are green or brown in color and bear a resemblance to twigs as a protective device. Walking sticks found in the tropics are the largest and most abundant. There are about 27 walking stick species in the southern regions of the U.S., compared with the 600 walking stick species that have been identified in Central and South America.

Walking sticks are related to leaf insects, which are also in the order Phasmatodea.

Physical description

Walking sticks have a long, narrow thorax and an extended abdomen. Some tropical walking sticks resembling tree twigs are more than 30 cm (11.8 inches) long, and others, much smaller, resemble leaves of plants. They are often wingless and characteristically have long legs adapted for walking. Among winged species, the front wings of some are short and leathery, whereas others have large, colorful hind wings that are kept folded over the abdomen. The head features mandibulate mouthparts and long antennae, and lacks tympanum (the hearing organ for insects). The female ovipositor is short and often concealed. Walking sticks are unusual among the insects in that they have the ability to regenerate legs and antennae.

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Both the form and coloration of walking stick insects serves as a form of protective mimicry, often with extraordinary detail. Some species can change their color to match that of the background by moving pigment granules in their epidermal cells. In addition to their camouflage, certain species have sharp spines, an offensive odor, or the ability to force their hemolymph (the invertebrate equivalent of blood and lymph), which contains toxic, distasteful chemicals, through special joints in the exoskeleton. In many species the eggs closely resemble seeds.

Read Britannica’s 9 Animals That Look Like Leaves

Natural history

While some walking sticks complete their life cycle in a single year, other species have a life cycle that can occupy two or more full years. In such species the eggs are not hatched until one or more years after they are laid, meaning that more than one winter or dry season is passed in the egg stage. For instance, a walking stick commonly found in the United States, Diapheromera femorata, often has some eggs that hatch the year following deposition and others that hatch after two winters have been passed amid dead leaves on the ground.

Of the walking stick species studied, most have eggs that look like small seeds and are dropped loosely on the ground. At least one species, however, attaches its eggs to foliage, and the southern two-striped walking stick (Anisomorpha buprestoides) scratches a depression in sandy soil with its front and middle legs, deposits eggs in it, and covers them with sand.

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Some genera (e.g., Carausius) rarely produce males. The eggs develop without fertilization in a process known as parthenogenesis.

Major species

The longest specimen collected, belonging to the species Phryganistria chinensis, measured 62.4 cm (about 2 feet). Other large specimens—measuring more than 30 cm (12 inches) in body length—belong to the species Phobaeticus chani and Phobaeticus kirbyi, which are native to Borneo.

The southern two-striped walking stick (Anisomorpha buprestoides) is a large, heavily bodied species in the southeastern United States. If handled, it sometimes forcibly ejects a milky fluid that is extremely irritating if introduced into the human eye. This species has a pair of circular pores on the thorax leading to reservoirs of the fluid; each reservoir has circular muscles that permit ejection of fluid without a general body contraction.

The North American species Diapheromera femorata may defoliate oak trees during heavy infestations.