The Stick Insect - A Sticky Subject

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Stick Insects (Phasmatodea) are exactly what the name suggests – insects that have the appearance of sticks. These masters of camouflage are found all over the world in different shapes and sizes, but are particularly numerous in the tropics and subtropics. There are about 3000 different kinds of stick insects in the world including several types of leaf insect.

They are some of the largest insects in the world, and specimens reaching up to 50cm with their legs outstretched, have been observed. Only recently discovered in 2004, Bactrododema krugeri is the largest of South Africa's 30 species of stick insect, measuring 30 cm. Leaf insects do not occur in South Africa.

Size really doesn't count in your favour, when you look like a plant part, and stick insects have developed a number of ways to avoid being accidentally eaten by herbivores, or intentionally by birds.

True to their name, these insects are supremely adapted to resemble small twigs, which assists them in avoiding detection. Some, such as Bactrododema, even develop lichen-like markings and thorny protrusions to this effect. Another adaptation is their nocturnal lifestyle where they remain almost motionless, swaying gently in the breeze, during the day and go about feeding at night when there are fewer birds around.

Stick insects don't bite or sting, they can't jump and only some species can fly, so when blending in doesn't work, they rely on startling an intruder into leaving them alone. This is usually done by shouting and waving their wings about – they emit a sharp noise, which sounds like the crumpling of newspaper, and will suddenly spread their coloured wing-like appendages, which is enough to make any bird think twice.

Interestingly, some stick insect species are parthenogenic, meaning the females do not need any male assistance for reproduction. They are able to lay fertile eggs without mating, which results in offspring that are exact replicas of the mother, and all female. If there is a male in the vicinity, mating will take place with about 50% of the eggs yielding male specimens. In this way the male population of stick insects is forever decreasing, and there is one species where males have yet to be discovered.

The seed-like eggs are usually scattered about on the ground, deposited into a small pit in the soil, or affixed to the stem or leaf of a plant and left to their own devices. The youngsters simply emerge after an incubation period of six months to a year and begin their life of deception without any parental assistance.


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Sunday, 21 October 2018