The life of Walkingstick insects

Walking stickWe have all seen “walkingstick” insects. They range from tropical forests to temperate grasslands and desert uplands where they feed on leaves. They vary in size from half-inch-long Timema cristinae of North America, to the formidable 13-inch-long Phobaeticus kirbyi of Borneo. This giant measures over 21 inches with its legs outstretched, making it one of the world’s longest insects, according to National Geographic. If you want to see what a really big one looks like, take a look at the photo here. See photos of the Arizona walkingstick here. Walkingsticks are in the taxonomic family, “Phasmatidae,” derived from the Greek word “Phasma,” which means phantom or apparition.

Walkingsticks employ crypsis, a combination of camouflage and mimicry to avoid being eaten by potential predators, mainly birds, reptiles, spiders, and bats. Walkingsticks are generally nocturnal and hide out during the day in foliage. DesertUSA notes: “For one graphic example, in the walking stick species called Diapheromera covilleae, which lives exclusively on the creosote bushes of the southwestern United States, the juvenile’s appearance and color match the new growth of the host plant… The adult male resembles a dead twig. The adult female, larger than the male, resembles a larger creosote twig.” See photo of mating pair here. Notice that the females are much larger than the males.

The Arizona-Sonora Desert Museum (ASDM) notes:

“When crypsis fails, stick insects often invoke secondary defensive behaviors. Insectivorous birds usually give a tentative, investigative peck to any novel object that might be food; initial caution minimizes the possibility of injury to the beak. A pecked walkingstick responds by immediately releasing its hold on the plant and falling to the ground, where it remains motionless for a long time, perhaps the rest of the day. Some species even jump to the ground when pecked.

“If grabbed by a predator, many phasmatids become rigid. The attacker may assume that is has found a stick and drop the insect. But what if the predator arrives at a different conclusion and tries to eat the insect?

“The majority of walkingsticks have yet another line of defense, glands that release distasteful or noxious chemicals. Some species regurgitate a foul liquid or leak blood from their leg joints. If a predator tastes the liquid or blood before mortally injuring the stick insect, it will likely release it. Even if the predator kills and eats a foul- tasting walkingstick, there is still a biological payoff. The predator will probably remember this unpleasant experience and avoid walkingsticks in the future. The sacrifice of one individual may spare that individual’s offspring and relatives from a similar fate.”

Walking sticks have suction cups and claws on their feet which enables them to wall up vertical surfaces and upside down.

ASDM also notes, “Immature walkingsticks possess an extraordinary defensive adaptation called autotomy. If its leg is grabbed by a predator, a nymph can shed the leg from a joint near its body. Better to give up a leg and leave than to hang around and risk your life! This sacrifice is not as extreme as it may seem, for the nymph can regenerate its lost limb within two weeks.”

Some walkingsticks have spines that resemble thorns on the host plants. Mimicry also extends to walkingstick eggs. To minimize predation, the eggs often resemble the seeds of the plant occupied by the walkingstick.

Walkingsticks have prodigious sexual stamina. Several sources cite the work of John Sivinski, a research entomologist in Florida, who studied walkingsticks while a graduate student at the University of New Mexico. From ASDM: “phasmatids mate for long periods of time. Diapheromera veliei, a species closely related to D. arizonensis, couples for 3 to 136 hours at one time, and in the extreme, a pair of Anisomorpha buprestoides may remain coupled for as long as 3 weeks.”

“Sivinski reasoned that because the transfer of sperm should require only a few minutes, protracted copulation must have a function other than fertilization. Following earlier work by Thomas Eisner, an eminent student of insect chemical defense mechanisms, Sivinski studied the predatory behavior of blue jays in the presence of both coupled and unmated walkingsticks to learn if the insects might pool their chemical defenses and hence survive longer together than apart. His research showed no survival advantage for males, but copulating females enjoyed significantly higher survival rates over non-copulating females.”

According to DesertUSA, only about 1 in 1,000 walkingsticks are male. That’s because “Lacking a partner, a female walkingstick can still lay fertile eggs, although all will yield female larvae. (Animals that can reproduce asexually are described as “parthenogenetic” by biologists.)”

This insect is more complex than it would first appear.