Insects and their Allies  

Blattodea: cockroaches

Methana marginalis

Methana marginalis (BLATTIDAE)

The general form of cockroaches varies little, however their size can range from only a couple of millimetres in length up to 70 millimetres for the Giant Rhinoceros cockroach from Northern Queensland. There are just over 400 species of cockroaches in Australia out of 4000 worldwide, the best known being the introduced pests which commonly inhabit houses, restaurants and sewers. All cockroaches have the following characteristics:

  • Oval and flattened body shape
  • Thorax covered by a large plate (the pronotum), which extends partly over the head
  • 2 pairs of membranous wings when present. Forewings are more sclerotised than hind wings. Wings are folded left over right when at rest
  • Long antennae
Cockroach Lifecycle
Cockroach Lifecycle
Geoscapheus dilatatus (BLABERIDAE)
Geoscapheus dilatatus (BLABERIDAE)

Life Cycle
Cockroaches have incomplete metamorphosis. Most species of cockroaches lay eggs in an ootheca (egg case) that is either deposited on or under suitable substrate, or carried attached to the genital region. The egg stage lasts from a few weeks to a few months. The young are active from hatching and resemble the adults but are usually lighter in colour and lack wings. The young cockroaches develop through a number of nymphal instars, which may range from 2 to 12 depending on the species and may take from a month or so up to 12 months to reach maturity. Some species may live for several years.

Much of the feeding habits of native Australian cockroaches is unknown, but it is likely the majority are omnivorous. Some species are known to feed predominantly on rotting wood while some species harbour symbiotic gut Protozoa that aids in cellulose digestion. The introduced domestic species appear to eat almost anything.

Cockroaches in Australia are widespread and adapted to both wet and dry environments. Most species are nocturnal and ground dwelling and are usually found hiding during the day in crevices, under bark, rocks or logs and in burrows. Some species may occur on plants or in litter and some also occur solely in caves or ant nests. Others are associated with human habitation.