American cockroach

Cockroaches are a primitive insect and have been around for millions of years. There are over 4500 species globally, but less that 30 of these species are considered as pests. In fact most cockroaches are considered beneficial, recycling decaying plant material. It’s only when they start to invade our living spaces, we consider them as pests.

With their association with disease and scurrying movement (not to mention the occasional flying cockroach!), homeowners want to know how to get rid of cockroaches and prevent cockroaches causing problems in the first place. With their reputation for being indestructible, it’s not always easy to get on top of a cockroach infestation. But with a bit of knowledge and the right products, homeowners can have a cockroach free home.

But it you’re looking for information on cockroaches and how to identify cockroaches, read on!


Cockroaches are a primitive insect. Cockroaches hatch from eggs into nymphs (young cockroaches) and go through several stages before becoming an adult. As the cockroach nymphs are similar to the adults (just smaller), this process is called incomplete metamorphosis. This is unlike the transformation of a caterpillar into a butterfly which is a complete metamorphosis (complete change in body form).

The length of the life-cycle depends on the species (generally large species have a longer life-cycle) and the temperature (higher temperatures mean a faster life-cycle). But the life-cycle  but can vary from between 3 months and 2 years. Adults cockroaches can live anywhere between……. The larger cockroach species have a longer life-cycle.

Cockroach eggs

Cockroach egg case - ootheca

Cockroaches don’t lay eggs but have egg cases. These egg cases can contain between 16 and 40 eggs, depending on the species – smaller species have more eggs. The eggs develop into nymphs inside the egg cases and emerge as live young. Some cockroach species, such as the German cockroach carry the egg case until just before hatching, others such as the American cockroach place their egg cases near a food source for later hatching.

Egg cases in cardboard boxes are a common way cockroach population get started in homes!

Baby cockroaches

“Baby” cockroaches are called nymphs. These are the young cockroaches that go through several nymphal stages or instars before turning into an adult. The first instars can be very small – newly hatched German cockroaches are only 3 mm long.

Depending on the species they may have between 6 and 14 instar stages before developing into the adult cockroach. During each stage they get bigger, with the wings gradually forming through each stage so they are fully formed in the adult.

White cockroaches

Every now and then a homeowner will spot a white cockroach. Alas this isn’t a new species or a freak of nature, but a normal part of the cockroach life-cycle. As cockroaches have a hard cuticle, they cannot grow continously. When they are ready to grow, they shed their skin. When they emerge their cuticle is white and soft. This gives them the chance to expand and grow. Over next 1-2 hours the cuticle darkens and hardens.

Flying cockroaches

Only the adult cockroaches have wings, but in some species only the male has functional wings and in others both the male and female cannot fly. Often the cockroaches will only fly in warmer weather and even then it is often a predator escape behaviour.


There are over 4500 species of cockroach globally, but only around 30 of them are considered as pests. Here in Australia there are 6 common pest cockroaches.

Pest cockroach species

Generally speaking the pest cockroaches can be broken down into “large cockroaches” and “small cockroaches”.

Large cockroaches

The large cockroach species typically live outside the home in drains and gardens, but will also set up home in the roof void and sub-floor. Generally these cockroaches come inside looking for food or moisture, or simply “by accident”. These cockroaches are often referred to as peridomestic cockroaches as they spend time inside and outside buildings.

The two most common large cockroach species in Australia are the Australian cockroach and American cockroach.

Small cockroaches

The small pest cockroach species typically live exclusively inside the home. As such, these cockroaches are often referred to as domestic cockroaches. The two most common small cockroach species are the German cockroach and brown banded cockroach.

Both these species are able to set up their home in the smallest of places – including door hinges, dishwashers, toasters, microwaves – and with their prolific breeding, they can be a lot more difficult to spot and control.


Other cockroach species

There are many non-pest cockroaches in Australia which do a great job as “re-cyclers” in nature. The “bush” cockroach and the giant burrowing cockroach are worth a mention…

Bush cockroaches

Green or mountain cockroach

The “bush” cockroach is a term given to many small native cockroaches which generally live outside in leaf litter but occassionally find their way into homes by accident. Some are small and brown (similar to the German cockroach), others are brightly coloured, like this mountain or green cockroach. Interestingly, many of the native cockroaches are active during the day, unlike the pest cockroaches which tend to be nocturnal.

Giant cockroach

giant burrowing cockroach


The giant burrowing cockroach – the heaviest cockroach in the world – is found in the rainforests of tropical Australia. Also called the rhinoceros cockroach or giant Queensland cockroach, these cockroaches can measure up to 8 cm long and weigh up to 35 g.  Unlike most other insects and cockroaches they don’t lay eggs but give birth to live young. They are very popular as pets!


  • Cockroaches will eat virtually anything, even each other!
  • As well as being nocturnal, cockroaches are very sensitive to vibrations and air movement, which is why the run away, often before the light is turned on.
  • Cockroaches are thigmotactic which means they like confined spaces. It also explains why the tend to run around the perimeter of rooms.
  • German cockroaches do not stray far from their hiding places – adults only travel 1-2 m from their harborage. The young  cockroaches do not leave their hiding place at all, eating the vomit and faeces of other cockroaches to survive!
  • The American cockroach has been measure running at a speed of 5.4 km/h, which would be comparable to a human running at 330 km/h.
  • Although many adult cockroaches have wings, most species do not fly. Adult American and Australian cockroaches will fly, but only in warmer weather.
  • The names of the pest cockroaches German, American, Australian don’t really described where they come from, as they are found in many countries. For example in Germany, the “German” cockroach is sometimes called the “Russian” cockroach!

Cockroach diseases

Given the places that cockroaches hide, including the sewer, drains and in the garbage, it is perhaps not surprising they are viewed as “dirty” animals. Indeed, cockroaches carry a range of diseases, including Salmonella, dystentry and polio, as well as a number of other bacteria that give rise to stomach upsets.

However, it is the shed cockroach skins and droppings that cause the biggest problem. In a cockroach infestations these can give rise to allergic reactions and asthma and is probably the highest cause of asthma in many inner city apartment blocks.

Image credits

Australian cockroach image used under Creative Commons 3.0. Lucinda Gibson & Ken WalkerWalker, K. (2007) Australian Cockroach (Periplaneta australasiae), availabile online at

Smoky brown cockroach image used under Creative Commons 3.0. Toby Hudson (Wikimedia Commons)