ZooNooz Article - march 2006

Cockroaches - friend or foe

Most of us think of cockroaches as pests - lurking in our kitchens, scuttling away when we turn on the lights, and almost impossible to get rid of. That may be true for a small handful of species, but there is far more to these little critters than just being kitchen scavengers.

Story and photographs by WARRICK ANGUS

Let's look at some basic facts. There are over 4000 known species of cockroaches in the world, and about 440 of them are native to Australia. Out of all these, only around 10 are considered pests - less than 0.1%! So what are all the other cockroaches doing? It's easy to find out - take a walk in your local bush and turn over a dead log. You're likely to find some ants, a millipede, and a couple of native cockroaches chewing away at the decaying wood.

Giant Burrowing Cockroach

Cockroaches have been roaming the earth for over 400 million years, and for most of that time they have been helping to break down dead trees, bark and leaves into soil. Most animals can't do this, but the cockroaches developed a way to digest the tough plant cellulose. They evolved a symbiotic relationship with protozoans (singlecelled animals) that reside in a section of their gut. These protozoans break down cellulose and provide the cockroaches with the nutrients.

Around the world today, cockroaches are so successful that they can be found everywhere on land except the polar regions. They range in size from the smallest at four millimetres, Attaphilla fungicola, which lives in nests with leaf cutter ants in South America, to the largest, Megaloblatta longipennis, from Columbia that has a body length over nine centimetres long and boasts a massive wingspan of 18 centimetres. Australia is fortunate to have the world's heaviest cockroach, the Queensland Giant Burrowing Cockroach, weighing in at up to 50 grams.

The Giant Burrowing Cockroach is so large and slow-moving that it is becoming a popular pet, and because it is wingless, many people often mistake it for a beetle. It spends the majority of its life burrowing deep underground, and has a specialised head shield that it uses as a shovel to push dirt aside as it digs with its large, powerful legs. These gentle giants venture out at night to collect dead eucalyptus leaves and carry them back to munch on in the depths of their burrows. And they are great parents. The female gives birth to live young (rather than laying eggs) and keeps her babies safe in a brood chamber at the bottom of her burrow until they are strong enough to build burrows of their own.

Wood Cockroach

Another native Australian cockroach that looks like a small burrowing cockroach and is found in Sydney is the Wood Cockroach. These cockroaches like to live in pairs and instead of burrowing deep underground, they live under rocks and dead branches, where they slowly decompose any rotting wood. Unlike burrowing cockroaches, these actually begin their life with wings. After establishing a home under a log, their new room-mates assist by chewing off their now redundant wings.

But what about those cockroaches we find in our homes?

American Cockroach

The two most common pest cockroaches are not from Australia. The larger of the two, the American Cockroach, is equipped with long antennae that enable it to sniff out any food scraps. Interestingly, this cockroach is not actually from America - it's from Africa. Similarly, the little cockroach that we often refer to as the German Cockroach, (the Germans call it the Russian Cockroach) is actually from Asia. Would you believe these cockroaches were given their common names as a result of war propaganda! We can't laugh - another pest species, the Aussie Roach, is also from Africa.

Even the pest species of cockroaches have amazing lifecycles. Not only can they survive for months without food, they can quite happily munch on anything organic - even the bindings of books. The American Cockroach has six long thin legs that enable it to run very quickly. If you have a closer look, you might also see two appendages on the end of the abdomen. These are 'cerci' and are used to sense vibrations and aid the cockroach in escaping from predators. When you try to swat a cockroach, these cerci feel the air pressure wave in front of your hand. The cerci send a message to one of many brains located in abdomen of the cockroach to tell the legs to run. Eventually, the head-brain and eyes kick in and the cockroach gets some direction into its random running.

So, next time you see a cockroach scurrying across your kitchen floor, just remember it's one of only a few non-house-trained species - its cousins are outside doing a fantastic job recycling.

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