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Cockroaches Biology

This page contains pictures and information about Biology of Cockroaches that we found in the Brisbane area, Queensland, Australia.
 
 
As we discussed in our index page, Cockroaches are classified as order Blattodea. They are primitive orthopteroid insects that are closely related with termites and mantids. Most of them are beautiful insects although this perception is always outweighed by their name "cockroaches". They have long spiny legs, their antennae are longer than their body. Their body is usually flat and broad so that they can squeeze into very tight places. Adults may or may not have wings. If they have, the wings are membranous with toughened forewings which overlap left over right. The head is small and pointing downwards, concealed under the pronotum. So sometime their thorax are miss-considered as their big heads. 
 
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Most cockroach adults have wings but some species are wingless. Some species the males are winded but females are wingless. For the winged species, they can fly although not very often. Instead all cockroaches are very good runners.  Most of them are active at night although some are active during the day time.
 
Cockroaches are scavengers, they feed on almost everything. Some species eat wood and digest cellulose with symbiotic bacteria in their gut. Those wood-eating cockroaches are very important in the breakdown of fallen logs in the wet forests. Those cockroaches seem to have some communal organization since they are commonly found in groups.
 
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Cockroaches are known to use perfume to attract mates and use pungent smell to repel predators. 
 
Mating preceded by courtship involving male and female pheromones. Copulating pairs remain joined for some time. 
 
Different families of cockroaches lay eggs in many different ways. In general most cockroaches produce groups of eggs enclosed together in a single capsules called o÷thecae. The o÷thecae sometime seen attached to the end of the female abdomen. Some cockroaches (Blaberidae, Panesthiinae) give birth to live young.
 
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Cockroach ootheca
 
O÷theca is a pale, soft egg-sac that hardens when exposed to air. The ovipositor valves serve as a mould that forms the o÷theca. The colour, size of the o÷theca are different depend on species. Each egg is in a shell surrounded by an air space. The O÷theca is carried for various lengths of time before it is deposited. They are usually attached on leaves or tree trunk. Some species hide it under the soil. 
 
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In the o÷theca young cockroaches hatch all at the same time. The young cockroaches swallow air, become inflated and force separation of the opening and emerge simultaneously.
 
Cockroaches develop in incomplete metamorphosisThe number of instars stages are different depends on species.  
 
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Nymphs resemble adults in body structure but lack of wings. However the body colours are usually different. 
 
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Cockroaches are preyed upon by many different predators including spiders, mantids, as well as reptiles, birds and mammals. Above picture shows a cockroach is captured by the Brown Huntsman. Cockroaches can escape capture by the use of defensive secretions.
 
The ootheca often serve as host of eggs-parasite wasps. Those ground-dwelling cockroaches are parasitized by parasitic Rhipiphoridae 

Reference:
1. Insects of Australia, CSIRO, Division of Entomology, Melbourne University Press, 2nd Edition 1991, p320.
2. Grasshopper Country - the Abundant Orthopteroid Insects of Australia, D Rentz, UNSW Press, 1996, p211.
3. Northern Territory Insects, A Comprehensive Guide CD - Graham Brown, 2009.
4. Order BLATTODEA Cockroaches - 30 June 1997, A.M.E. Roach & D.C.F. Rentz, CSIRO Entomology, Australian Faunal Directory, Australian Biological Resources Study.

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Last updated: May 01, 2011.