Mardoo said:
Lots of species of cockroaches. We have ones in our house in VIC that only eat dead leaves and rotting wood. Says a lot about that drainage problem under the house the landlord can't be fucked with.
There are many species of cockroach in Aus.
The ones you describe are most likely the Australian native cockroach and although they still carry what may be considered dangerous germs, they generally live outside in mulch as you say, or it is common to find them in compost bins and old disused septic pits pipes and drains.
The species considered the worst is the German cockroach because of its ability to breed in extremely large numbers.
It is very happy to live in kitchens and enjoys areas such as refridgerator motors where it is warm and has a constant water supply by the de frost action of most modern fridges.
They can also live in microwave ovens, hot water services and electric stoves or as it has been said above, any crack or crevice in furniture, floor boards, built in cupboards etc.
Commercial kitchen premises can be plagued with cockroach infestations due to the fact that most cockroaches are introduced to the area by travelling in the folds of cardboard cartons when goods are delivered from wharehouses.
A common source of introduction into a private home apart from the above is the purchase of second hand whitegoods, fridges, in particular can be a real problem.
Quite often, refridgerator repair shops can be infested with cockroaches by accepting an appliance that has an infestation for repair.
Once in the workshop they will then invade other appliances in the area and then travel to their new home when the fridge has been delivered back to its owner.
Repair shops are generally quite aware of this occurence and if a fridge is delivered to them with cockroaches evident, then in some cases that client will foot the bill for treatment as required.
Chemical treatment is often frowned upon by some but in Australia we have some of the most strict laws regarding the make up and the use of insecticides in the domestic and commercial pest management situation.
As I had explained in a post above, the new chemicals that are constantly becoming available to the industry, if used correctly are a lot less of a threat to our health than the diseases that can be spread by cockroaches.
Take the time to actually read the attachment or do some research if you have any concerns.
http://cleanhealthysafe.blogspot.com.au/2015/03/cockroaches-spread-infectious-diseases.html
Any cockroach infestation, particularly in a domestic or commercial kitchen can be extremely dangerous and should not be looked upon lightly unless, of course, you dont care about you or your families health.