Key to Australian Freshwater and Terrestrial Invertebrates
Phylum Arthropoda
Subphylum Hexapoda
Class Insecta
Order Blattodea
Common name: cockroaches
Overview
The Blattodea, or cockroaches, are a distinctive group of insects with an oval, flattened body and thorax and part of the head covered by a large plate (the pronotum). They have chewing (mandibulate) mouthparts, long antennae, prominent cerci at end of the abdomen, and, typically, two pairs of more or less membranous wings, the forewings more sclerotised than the hindwings. Several species are wingless (apterous) or have reduced wings (brachypterous). Cockroaches range enormously in size, from the small, fragile 3 mm long Nocticola sp., to the giant rhinoceros cockroach from northern Queensland, Macropanesthia rhinoceros, which can reach up to 80 mm in length and is among the heaviest of insects, weighing 20�30 g. Among the best-known and frequently encountered cockroaches are the introduced pest German (Blatella germanica) and American cockroaches (Periplaneta americana) that commonly inhabit human structures.
Distribution and diversity
Cockroaches can be found across Australia in a wide range of habitats from tropical rainforests to the arid centre. The Australian cockroach fauna numbers 534 described species in 71 genera from five families. Worldwide there are about 4,000 species in 460 genera. At least 90% of the Australian fauna is considered endemic; at least 50 species remain to be described.
Life cycle
Sperm transfer In cockroaches is direct from male to female. The females of most species lay their eggs enclosed together in an egg case or capsule (ootheca), which they carry around, attached to the genital region, or drop on the ground, glue to bark or some other substrate and sometimes cover or bury in the soil. The eggs hatch within a few weeks to a few months. Nymphs resemble the adults but are usually lighter in colour and lack wings. Some species give birth to live young (viviparous). Nymphs moult and develop through a number of instars, which may range from 2�12 depending on the species. Complete development can take from four weeks to 12 months, with some species living for several years. Facultative parthenogenesis has been reported for most pest species, but it not known if any native species can also develop this way.
Feeding
Little is known of the feeding biology of most native Australian cockroaches. It is likely that the majority are omnivorous, feeding on leaf litter and other detritus and plant material. Some species are known to eat rotting wood and many have symbiotic gut protozoa that aid in cellulose digestion. The introduced pest species feed on almost anything that is available.
Ecology
Cockroaches in Australia are widespread and range from ground-dwelling species living in leaf litter, under bark, logs, stones or burrows in the soil to arboreal species found in trees and shrubs. Most appear to be nocturnal and ground-dwelling, but the biology of the vast majority of Australian cockroaches has not been studied. The often abundant wood-eating cockroaches and those that burrow and feed on fallen leaves are ecologically significant, and undoubtedly represent a vital part of the food web, being important for breakdown of plant-material and maintenance of soil fertility. Some species are diurnal and can be seen moving about on the ground or perched on flowers and leaves in the sun during the day. Some of these are brightly coloured and patterned, and are considered mimics of highly toxic lycid beetles (Coleoptera: Lycidae). Other cockroach species can escape predation by excreting a noxious fluid; some use camouflage. Across the Australian continent several species are exclusive cave dwellers and lack eyes and pigmentation and have the wings reduced or absent. With one or two exceptions, native Australian species do not cohabit with humans and are of little economic importance. However, those exotic pest species associated with human habitation can contaminate food and are capable of transmitting diseases that affect humans. These species are more commonly a problem in warmer regions where populations can reach extremely large numbers.
