stick insect

Stick Insect Facts

Physical characteristics of stick insects

color

• Brown
• grey
• tan
• green

skin type

shell

A stick insect's entire life is devoted almost entirely to crypsis' unique strategy: the ability to blend into its natural environment, which may include different kinds of bark, moss, leaves, lichens, and twigs. What sets the stick insect apart from other mimic species, however, is that its camouflage is more than just an outward affectation. The insect actually camouflages itself as a twig or leaf of its host plant. Evidence suggests it has even honed its ability to mimic the motion of a tree branch swaying in the wind to fend off particularly keen predators.

Given the large number of species within the Fusaridae order, stick insects can exhibit a variety of morphological sizes. The smallest known species — Timema cristinae in North America — is just half an inch across, according to National Geographic. The largest species – the daunting Phryganistria chinensis Zhao in China – is more than two feet long! Just for comparison, a typical adult foot is about 12 inches long. Stick insects are sexually dimorphic, so on average, females are considerably larger than males.

Despite the wide variation in size between species, stick insects do share many common features, including elongated antennae, compound eyes, cylindrical or flattened bodies, multiple movable mouthparts, segmented legs, and short or Highly shrunken wings. While typical stick insects look fairly drab green or brown, certain species are wrapped in bright and conspicuous shades of yellow or red to signal to predators how unappetizing their taste is. In fact, the males of a new species recently discovered in Madagascar turn blue during mating season.

Some truly bizarre stick insect species display a variety of unexpected traits, including well-developed wings, sharp spines on the legs, false buds, lichen-like growths, and the ability to change pigmentation to adapt to their surroundings. These defense mechanisms are tuned to help it live a life of relative solitude in harsh environments.

Stick insects are widely distributed in temperate, tropical and subtropical regions of all continents except Antarctica. They live almost exclusively in grasslands, woodlands, and forests. The greatest number of stick insect species are found in South America and Southeast Asia, but a disproportionate number appear to occupy the large island of Borneo in the Pacific Ocean. Borneo is home to a wide variety of rare and diverse animal species, many of which are found nowhere else in the world.

In order to avoid predation, stick insects are mainly nocturnal in nature. They spend most of their time lying motionless on or under plants, only coming out to feed at night. Many species seem to be well adapted or at least to some extent selected for their host plants (which also tend to serve as food sources).

Stick insects are low on the food chain. It is constantly at risk of becoming prey for birds, primates, reptiles, spiders, small mammals and even other insects. Bats are perhaps the most dangerous predators. Their echolocation easily negates the insect's greatest strengths, its camouflage and sneakiness.

If its shell is blown, the stick insect may fall back on another of its many defense mechanisms to deter a hungry predator. While each species may be different, common traits may include sharp spines used to attack predators, noxious odors expelled from glands, and even nasty chemicals in the blood, which it forces through the exoskeleton seam. Some species have the ability to detach or amputate limbs at joints where they are grasped by predators. This phenomenon, known as limb autotomy, is only a temporary setback, as the insects regrow the missing limb over time.

If all else fails, the stick insect may resort to the ever-proven tactic of trying to startle or scare away predators by being loud or aggressive. The presence of colored wings or unusual features can enhance the effectiveness of this display. If the predator is momentarily confused, the stick insect will drop off and hide in the bushes to evade detection.

Despite their global ubiquity, stick insects can be vulnerable to habitat destruction, pesticide use, and human encroachment. Without the protection of plants or trees, stick insects are vulnerable to predators.

Reproduction of stick insects is perhaps the most complex aspect of their existence. Reproduction begins with long and protracted courtships that may last days or even weeks at a time. During these uninterrupted mating sessions, the insects will remain attached to each other and rarely let go. Because stick insects don't necessarily rely on visual cues, they release chemicals in the air to attract mates.

Many stick insects have the remarkable ability to produce female offspring from unfertilized eggs in the absence of any males. This type of asexual reproduction is called parthenogenesis. It produces an exact copy of the mother. While some species may prefer to reproduce almost exclusively this way, breeding methods are known to fluctuate within populations over time. The origin of sexual reproduction is unknown, so the emergence of parthenogenesis as a reproductive strategy is a highly unusual phenomenon that has aroused the curiosity of many scientists.

Regardless of the reproductive utility of parthenogenesis, a single female stick insect can eventually lay hundreds of eggs in a short period of time. Because eggs are highly vulnerable to predators, stick insects have evolved a variety of strategies to deal with the threat. Females may choose to place each egg far apart on the ground below, or lay eggs in hard-to-reach discrete hiding spots, or even attach the eggs to leaves or plants.

Stick insects rely on a method of reproduction called hemimetabolic. This is an incomplete form of metamorphosis in which the insect's life cycle goes through three distinct stages. The first stage of the life cycle occurs entirely within the egg, with developmental cycles ranging from a few months to a year.

Once a stick insect emerges from its egg, it begins the second stage of its life cycle: the nymph stage, in which the insect resembles a young version of a mature insect. The stick insect can't transform all at once — it lacks the pupal stage common to many other insects — so the larva must grow gradually through a series of intermediate stages to reach full maturity. At various times throughout the process, the insect sheds the old exoskeleton and then creates a brand new one. The time between molts is called the first instar.

The nymph does not simply discard its old exoskeleton, but continues to consume it. This is done for two reasons. First, the exoskeleton is an excellent source of protein. Second, the insect can hide all evidence of its molting from observant predators.