bcm1 October 2007

Social Life of Cocky
The male cockroach

Physically, the cockroach is so well adapted to life that it has not changed for 400 million years or more, although these fossils of mine [photos 2, 3] are only 120 million years old. But how has its social life helped them to survive?

There are three main aspects of cockroach social life:

• Protection

• Fighting

• Communication

These three social characteristics change through life, as shown on the following diagram [figure 1]. The progression from baby to adult goes from submissive to aggressive, silent to communicative and protected to protecting. Through this article, you can see this progression through the life of one individual, Cocky. He is a Madagascan Hissing Cockroach, or Gromphadorhina oblonganota. Cocky is a real cockroach and he is one of my pet cockroaches.

The life line [Figure 2] shows you what stages there are.

This is mirrored by the photo [photo 4], which shows the egg case, nymphal stages and adult, and by the subheadings in the rest of this article Cockroaches can live for four years (twice as long as the average gerbil). Living longer means having more time to reproduce - and more time to reproduce means that they can contain the ootheca for longer.

Mother

Cocky is protected by his mother as an egg, so we start before he is born – as an egg case extruded by his mother [photo 5]. She twists the ootheca round [photo 6] so that it lies along the abdomen instead of across it. The advantage is protecting the young for longer. She keeps it safe inside her until it is ready to hatch, with Cocky’s 30-60 brothers and sisters. Even if you boil the ootheca, the eggs will still hatch out and become perfectly normal cockroaches.

Nymph

Small roaches are sheltering under the adults, mainly directly under them [photo 7]. They use the spines on the adults’ legs to protect them, as well as the adult’s hissing warning system. They shelter under any adult for protection. Cocky can’t communicate through hissing yet: he’s not physically ready: he is not strong enough to propel air through his spiracles fast enough to make the hissing sound.

Young male

Young cockroaches do not practice fighting, unlike most young animals. They are still protected rather than protecting.

Final moult

Cocky’s final moult [photo 8]. The exoskeleton is eaten for its important nutrients. When Cocky had his final moult, he started to fight, and to hiss to attract a mate.

They have several different hisses with different meanings, and Cocky can now join in with these to protect the colony, and to deter predators. Its main predators are lemurs, tenrecs and huge bush crickets. Its predator warning hiss is fairly low, but not quite as low as the mate attraction hiss. The highest hiss is a warning to the colony, which warns the colony of danger. After he had his final moult, he started to protect babies and fight for dominance and females.

Dominance

Here is Cocky, now an adult, fighting with Mr Madder, the dominant male of my colony [photo 9]. Cocky is the small one on the left.

How they fight:

• Push fight: photo 8 showed Cocky and Mr Madder push fighting. Cocky is too small to dominate, but he tried!

• Attack antennae: they attack each others’ antennae to prevent mating: they cannot smell the females without antennae. Cocky has already lost half his left antenna.

• Hissing attracts females: hissing is important as females don’t mate with silent males. We know this because an experiment was done where an entomologist bunged up the hissing spiracles with glue so that they couldn’t hiss and were forced to live outside the social group.

• Try to gain height advantage: you can see in this colony at the Oxford University Natural History Museum [photo 10] which is the dominant male because he is high up, looks ready to push down any intruding male, he is big and both of his antennae are complete.

Old Age

Cocky is not yet old. He is still a fighting adult, still trying to dominate. As they age, they become less protective, less communicative and less aggressive. This photograph [photo 11] shows how much the size of the cockroach changes throughout the life of the roach. They have come a long way from the newly emerging nymph to the large male shown here.

So, you see, a cockroach isn’t all just icky. It’s a very social creature.

It is so well adapted to life that it has not changed for 400 million years or more.

The three aspects which make them social have helped them adapt and survive.

Protecting each other and using fighting and hissing to select the best mate has helped them become successful. Even though cockroaches have not needed to change physically, they have become widely diverse, to fill all of the little evolutionary places and all types of habitat you could possibly think of all round the world: and being social has helped them to do this.