Phasmatodea, also called Phasmida
The bizarre-looking, slow-moving, plant-eating walking stick - among the
most intriguing of the insects - has raised camouflage, mimicry and defense to
a veritable art form. Through an adaptation called "crypsis," it blends
in so perfectly with its natural habitat that it often goes completely undetected
by would-be predators. Its taxonomic family name, "Phasmatidae," derived
from the Greek word "Phasma," means, appropriately, phantom or apparition.
Its other common names - for instance, specter, devil's horse, devil's darning
needle and witch's horse - reflect its hold on the human imagination.
Common Questions About Walking Sticks
- How do I recognize a walking stick insect?
- Can a walking stick cause injury?
- Do walking sticks make good pets?
- How do I control walking stick infestations?
Appearance and Anatomy of a Walking Stick
- Usually several inches in length (range from 1/2 inch to 13 inches)
- The body is thin like a twig,
- Has an exoskeletal body with three parts: the head, the thorax and the abdomen
- Usually green, brown or gray in color - of its immediately surrounding leafy habitat.
- The head contains the brain and its chewing mouth parts
- Insects breath through their thoracic and abdominal spiracles not through their mouths like humans
- Two compound eyes, which have multiple lenses and photosensitive cells that can resolve images, motion and color
- Two antenna, which can sense temperature variations and chemical odors and can probe physical surroundings.
Thorax contains vital organs
- Thorax serves as the attach points for the insect's three pairs of long, spindly, jointed legs, which have claws and suction pads on the feet
- Two pairs of wings, which occur only on some species.
- Abdomen contains the digestive tract and reproductive organs
- Abdomen typically extends for the second half of the length of the body.
Range, Habitat and Forage
Walking sticks occur essentially throughout the temperate and, especially, the subtropical and tropical regions of the world. They inhabit most of the United States, occurring most abundantly in the southern half of the country. Species make their homes among preferred plants. For instance, southern California's and Arizona's western short-horned walking sticks live among their favored globe mallow, burroweed and deerweed. Texas' giant stick insects choose river bottoms with their favored oaks and grapevines. Walking sticks may feed on a single, preferred species of broad-leaf plant or a variety of broad-leaf plants. In heavy infestations, walking sticks may denude a food plant, although the insect's reach is usually limited by the absence of wings.
When mating, male and female walking sticks may remain coupled for several hours, several days or sometimes even weeks. During this time, the male, usually smaller than the female, may be guarding his mate or, at least, his sperm. The female may lay one to several eggs per day, attaching them to the bark and leaves of her home plant, burying them in the soil below, or simply discharging them to the leaf litter.
The female's eggs, which often closely resemble her primary host plant's seeds, have lid-like structures through which the nymphs will emerge within a matter of months or years, depending on species and conditions. Typically, a walking stick will live for a year, but it may live for several years, particularly in captivity.
General Taxonomy of the Walking Stick
Walking sticks seem to defy neat taxonomic classification, especially at the lower taxonomic levels. They are generally grouped with the order of insects called "Orthoptera," which also includes the leaf insects, praying mantis, cockroaches, grasshoppers and katydids. Earlier, stick insects were all placed into the Phasmatidae family, which included both the stick insects and leaf insects (insects that resemble leaves). More recently the stick insects have been re-grouped by scientists into four families, including common walking sticks, winged walking sticks, striped walking sticks, and Timemas (smaller, thicker, flatter-bodied) walking sticks. Altogether some 2500 to 3000 species have been described - often incompletely and inadequately, according to the literature - many more species await discovery and description.
Stick insects are very rich in nutrition and make excellent meals for various predators. Predators include: birds, reptiles, spiders, bats and primates. Since bats hunt at night by using echolacation, they can easily prey on the stick insects by tracking the noise they make. The stick insect's camouflage does not help defend them against bats.
Camouflage and Defense
The walking stick employs an array of strategies to disguise and defend itself from predators. Some species can bite or pinch with their thorny legs.
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, according to John Sivinski, Natural History Magazine, June, 1992. The adult male resembles a dead twig. The adult female, larger than the male, resembles a larger creosote twig.
In addition to camouflage, the insect employs an array of other defensive tactics. It may, for a few examples:
- Remain perfectly motionless, especially during the day, with its forward and back legs outstretched, as if it were a twig of its host plant.
- Flex its legs, swaying its body randomly from side to side, mimicking a lightly blowing twig
- Suddenly flip open its wings (if it has wings) to startle a threatening predator
- Play dead, stiffening its body, and fall to the ground
- Sacrifice a leg grabbed by a predator (it can regenerate the leg within a few weeks)
- Feed nocturnally, when the risk of detection by a predator is lower
- Discharge a foul-tasting blood from its leg joints
- Regurgitate an evil-tasting liquid through its mouth
Though walking sticks are not known to bite, some walking stick species, for instance, the American stick insect (Anisomorpha buprestoides), found in the southeastern United States, can spray a milky kind of acidic compound from glands on the back of its thorax. It aims the spray with surprising accuracy, unerringly hitting the face of a perceived predator, including humans or pets, from one to two feet away. The compound causes intense burning and even temporary blindness should it strike the eyes. Should that happen to you or your pet, you should drench the eyes with cool water and seek medical attention promptly.
A Few Walking Stick Facts
As indicated by the fossil record, the walking stick has evolutionary roots that reach back more than 200 million years, to the Triassic geologic period
Walking sticks have suction cups and claws on their feet which enables them to wall up vertical surfaces and upside down
Approximately 1 in 1000 stick insects is male
The walking stick is the longest of all the modern insects, with a documented specimen from Borneo, for example, measuring more than 18 inches in length.
The giant walking stick, Megaphasma denticrus, which ranges from New Mexico eastward, is perhaps the longest in the United States, measuring six or seven inches in length.
Lacking a partner, a female walking stick can still lay fertile eggs, although all will yield female larvae. (Animals that can reproduce asexually are described as "parthenogenetic" by biologists.)
The females of some species rely on ants to disperse their eggs, a process called "myrmecochory."
A New Guinea species has heavily spined back legs that native peoples used as fishhooks.
Author: Jay Sharp
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