- Written by Nadia O’Carroll
There are a handful of cockroach species that follow and thrive in human habitation throughout the world, and it is these pest species that we see scuttling around our houses. They are extremely hardy, hide effectively during the day, can eat almost anything and reproduce quickly. Cockroaches’ indiscriminate feeding in unsanitary locations contaminate them, and what they touch, with bacteria. It has not been conclusively proven that they transmit human diseases, however they definitely cause allergies in some people.
Since we often see the pest species and hardly ever see the harmless wild species, it is not surprising that cockroaches have such a bad reputation.
Cockroaches are ancient insects; fossilised specimens from 320 million years ago appear the same as their modern descendants. There are some basic characteristics common to all cockroach species including oval, flattened shape; plate covered thorax; membranous wings; compound eyes; long attenae and bristly legs. As would be expected when such a large number of species inhabit a wide range of habitats there are also many differences – some can fly and some are flightless; some are nocturnal and some diurnal; some are dull brown while others can be brightly coloured orange, yellow, red and blue. Their reproduction can also vary – most carry or deposit an egg case, hatchlings then go through nymph stages until they become adults; some species produce live young and there is one species that reproduces parthenogenetically (ie the female produces young by herself without male participation)
In Australia the five household pest species are exotic, introduced cockroaches, their common names are the German, the American, the Oriental, the Asian and the Brown banded cockroaches. There are over 430 Australian native species, one of which, the Rhinoceros Cockroach (also called Giant Burrowing Cockroach) is gaining popularity as an insect pet. It is the world’s largest cockroach, and can reach 80 mm in length and 30g in weight. This cockroach may have a lifespan of 10 years and produces live young. In the wild it can burrow a metre underground.
Cockroaches have some remarkable characteristics. They have highly sensitive motion sensors on their back legs – these tiny hair like structures (cerci) can detect the slightest motion of air which is instantly communicated to a nerve centre in the back legs, it is estimated that the time between the air movement and resultant leg movement is 40-50 thousandth of a second. Experiments indicate that cockroaches communicate, cooperate, make group decisions and have memories that work better at night than in the morning.