R5574 Native Australian cockroach



This is a colour photograph of Mitchell's diurnal cockroach ('Polyzosteria mitchelli'), a native Australian cockroach, among ground detritus. The bright colourful markings of this cockroach are visible. (Classification - Phylum: Arthropoda, Class: Hexapoda, Order: Blattodea, Family: Blattidae.)

Acknowledgements: The original photo in this digital resource was provided by CSIRO. Photograph by D Rentz.

Educational value
This asset shows the characteristic body shape and form of a cockroach, a ground-dwelling insect - cockroaches all belong to the Order Blattodea, and are characterised by an oval, flattened body shape and a triangular-shaped head that is largely concealed under a thoracic plate (the pronotum); this head and body shape of cockroaches adapts them for moving around through tight crevices found in bark, twigs, rotting logs and rocks; most Australian species of cockroaches are flightless, and have long, spiny legs specialised for running and digging; they have primitive, generalised mouthparts for scavenging on a range of food items among the leaf litter and soil.
It displays some of the sensory receptors relied upon by cockroaches to obtain information about their environment - the long, thin antennae, and long, spiny legs of cockroaches are covered with many tiny hairs that act as touch and chemical receptors; the cockroach body also contains many external sensory hairs and at the posterior end bears a pair of prominent cerci, which are feeler-like extensions stimulated by air currents and ground vibrations; all these sensory receptors are used by cockroaches to help them to locate food and suitable habitats, avoid predators and communicate with potential mating partners.
It shows the bright, colourful patterns of the native Mitchell's diurnal cockroach - unlike most native Australian cockroaches, which are nocturnal and usually black or reddish brown, Mitchell's diurnal cockroach is active during the day, has small transparent windows in the edges of the plates covering its thorax and distinctive bright yellow and blue markings on its relatively large body; the bright colours of this flightless cockroach work in several ways as a defence mechanism against predators such as birds, lizards, frogs and small mammals active during the day; they can be flashed to startle the predator, or a warning sign that the cockroach is either poisonous or bad-tasting, or they may simply mimic the colour patterns of another poisonous insect; they can also act as a form of camouflage known as disruptive colouration where the outline of the cockroach becomes indistinct against the dark colours of its leaf litter habitat.
It demonstrates an insect that undergoes incomplete metamorphosis during its life cycle - the eggs of most species are laid into a protective egg case, or ootheca, usually deposited on the ground or buried in the soil, or in some species carried attached to the posterior end of the female; the juveniles hatch out of the eggs after a few weeks or months depending on species; they resemble the adults except they are smaller and generally paler in colour; the juveniles then develop through nymphal stages, which may take as little as one month or as long as one year, before becoming adults.
It illustrates a native Australian cockroach that is not regarded as a pest - some cockroaches have been infesting human habitation at least since storage of food began; the most common pest cockroach in Australia is the introduced American cockroach ('Periplaneta americana') that can live for several years and feeds on almost any organic matter in our houses; although people often associate all cockroaches with the house-infesting species, they are just a small proportion of all cockroaches, with fewer than 1 per cent of species considered pests; most cockroaches are important decomposers in their natural habitat.
Diurnal behaviour
© Curriculum Corporation and The Australian National Insect Collection, CSIRO Entomology, 2008, except where indicated under Acknowledgements