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Mantis religiosa
4 inches is probably exaggeration. More like 2.5 inches or over for female Mantis religiosa. Different subspecies of Mantis religiosa vary in size and less food will make them much smaller. I do not know if Mantis religiosa live in Forests but maybe. I am not sure if they live in Australia, do they?
Mantis religiosa live naturally in tropical parts of Asia too not just temperate.
That website for a reference shows what looks like a Stagmomantis limbata and not a M. religiosa so probably not trustworthy.
Thought Mantis Religiosa is European species, there exist one species from native Asia/Srilanka, that is mantis Religiosa Asiatica :)