Stick insect

The Phamatodea order of insects are an amazing study of clever camouflage and evolution.

Something moved beside me and I thought it was a grass / twig. Closer inspection revealed this beauty to me. It is an Indian Stick Mantis. Resembling an alien species more than an insect, the Aethalochroainsignis, is a species of praying mantis found in India.

As its name suggests, the stick insect resembles the twigs among which it lives, providing it with one of the most efficient natural camouflages on Earth. It and the equally inconspicuous leaf insect comprise the Phasmatodea order, of which there are approximately 3,000 species.

Phasmids generally mimic their surroundings in color, normally green or brown, although some species are brilliantly colored and others conspicuously striped. Many stick insects have wings, some spectacularly beautiful, while others resemble little more than a stump. A number of species have spines and tubercles on their bodies. Phasmids can be relatively large, ranging from 1.5 centimeters (0.6 in) to over 30 centimeters (12 in) in length. Females of the genus Phobaeticus are the world’s longest insects, measuring up to 56.7 centimeters (22.3 in) in total length in the case of Phobaeticuschani, including the outstretched legs.The heaviest species of phasmid is likely to be Heteropteryxdilatata, the females of which may weigh as much as 65 g (2.3 oz).

Stick insects have two types of pads on their legs: sticky “toe pads” and non-stick “heel pads” a little further up their legs. The heel pads are covered in microscopic hairs which create strong friction at low pressure, enabling them to grip without having to be peeled energetically from the surface at each step. The sticky toe pads are used to provide additional grip when climbing but are not used on a level surface.

The life cycle of the stick insect begins when the female deposits her eggs through one of these methods of oviposition: she will either flick her egg to the ground by a movement of the ovipositor or her entire abdomen, carefully place the eggs in the axils of the host plant, bury them in small pits in the soil, or stick the eggs to a substrate, usually a stem or leaf of the food plant. A single female lays from 100 to 1,200 eggs after mating, depending on the species. Many species of phasmids are parthenogenic, meaning the females lay eggs without needing to mate with males to produce offspring. Eggs from virgin mothers are entirely female and hatch into nymphs that are exact copies of their mothers. Stick insect species that are the product of hybridization are usually obligate parthenogens, but non-hybrids are facultative parthenogens, meaning they retain the ability to mate and their sexual behavior depends on the presence and abundance of males.

Phasmatodea eggs resemble seeds in shape and size and have hard shells. They have a lid-like structure called an operculum at the anterior pole, from which the nymph emerges during hatching. The eggs vary in the length of time before they hatch,ranging from 13 to more than 70 days, with the average around 20 to 30 days. Some species, particularly those from temperate regions, undergo diapause, where development is delayed during the winter months. Diapause is initiated by the effect of short day lengths on the egg-laying adults or can be genetically determined. Diapause is broken by exposure to the cold of winter, causing the eggs to hatch during the following spring. Among species of economic importance such as Diapheromerafemorata, diapause results in the development of two-year cycles of outbreaks.

Stick insects, like praying mantises, show rocking behavior in which the insect makes rhythmic, repetitive, side-to-side movements. The common interpretation of this behavior’s function is it enhances crypsis by mimicking vegetation moving in the wind. However, these movements may be most important in allowing the insects to discriminate objects from the background by relative motion. Rocking movements by these generally sedentary insects may replace flying or running as a source of relative motion to help them discern objects in the foreground.Mating behavior in Phasmatodea is impressive because of the extraordinarily long duration of some pairings. A record among insects, the stick insect Necrosciasparaxes, found in India, is sometimes coupled for 79 days at a time. It is not uncommon for this species to assume the mating posture for days or weeks on end, and among some species pairing can last three to 136 hours in captivity.

Found predominantly in the tropics and subtropics—although several species live in temperate regions—stick insects thrive in forests and grasslands, where they feed on leaves. Mainly nocturnal creatures, they spend much of their day motionless, hidden under plants. Many stick insects feign death to thwart predators, and some will shed the occasional limb to escape an enemy’s grasp. Others swipe at predators with their spine-covered legs, while one North American species, Anisomorphabuprestoides, emits a putrid-smelling fluid.

Research has been conducted to analyze the stick insect method of walking and apply this to the engineering of six-legged walking robots. Instead of one centralized control system, it seems each leg of a phasmid operates independently.