Spotting a cockroach scuttling across your kitchen floor is pretty disgusting, and most of us would instinctively try to stamp on it before it hides somewhere we cannot reach it. It is even more horrifying when you lift your foot and the roach continues on its journey as if nothing has happened. How can they do this? Here we will explore the fascinating world of cockroach skeletons and their remarkable ability to survive.
Cockroach Evolution
Cockroaches are survivors and have been on this planet a lot longer than we have. They even predate dinosaurs by more than 150 million years. In all that time, they have changed very little, yet have diversified and adapted to many different habitats. Today, there are over 4,000 cockroach species, and many of them live in forest habitats. However, they have also been remarkably successful at adapting to live in human homes and other buildings. In particular, the German cockroach (Blattella germanica) and the American cockroach (Periplaneta americana) were brought from Africa to the Americas on slave ships. They are now common household pests and frequently get stamped on! Sharing a home with a cockroach is not much fun; they can spread bacteria such as Salmonella and as they walk, they leave a trail of fecal matter. As if that were not bad enough, the proteins in their saliva can cause allergies and trigger asthma in susceptible people.
How Cockroaches Survive Your Shoe
Cockroaches are insects belonging to one of several families in the Blattodea order. Most of them are around the size of your thumbnail, but there are some larger species. All of the species have a broadly similar body shape. Their heads are relatively small, and they have a broad, flattened body which is divided into a three-segmented thorax and a ten-segmented abdomen.
Cockroaches do not have bones like we do. Instead, they have a tough exoskeleton, which is like a hard casing around their body. It provides protection, serves as a muscle attachment point, and prevents fluid loss. The exoskeleton is made of calcareous plates called sclerites, which consist primarily of chitin (made of sugar and nitrogen). These plates are tough but, crucially, they are also bendy. So, they efficiently transmit energy and overlap as your shoe presses down on the cockroach’s back. Research has shown that the American cockroach can withstand a compression of 900 times their own body weight thanks to this mechanism. Having been compressed to this extent, the cockroaches in the study were still able to move normally and showed no signs of injury. The scientists suggested that it was soft arthrodial membranes joining the sclerites together and allowing them to move that produced this impressive compressibility. When it comes to cockroach exoskeletons, flexibility may be more important than strength.
The Best Time to Stamp on a Roach
Cockroach nymphs can be injured before their exoskeleton hardens.
©bamgraphy/Shutterstock.com
There are some points in the cockroach’s lifecycle when they are more vulnerable to getting stamped on. Taking the American cockroach as an example, they have three life stages: the egg, nymph, and adult. Females lay between 12 and 16 eggs, and they are encased in secretions produced by the colleterial glands to form a protective pouch called an ootheca. The female either carries this around with her or attaches it to a surface. It has a hard protein coating, but if you stamp on it, you would probably destroy it.
The nymphs that emerge from the egg cases are white but then turn greyish brown as their exoskeleton hardens. They will undergo between 6–14 molts (depending on environmental factors and food availability) before they reach adulthood, and the period of growth between the molts is called an instar. Once the cockroach reaches sexual maturity, it stops growing and molting. Each molting process is triggered by hormones produced by the cockroach’s body when it has reached the physical limits of its old exoskeleton. After molting, most roaches are easily injured until a hormone (bursicon) causes their exoskeleton to darken and harden. So if you are going to stamp on one, this is when you should do it!
No Head – No Problem
Even if you manage to severely damage the cockroach’s head (or decapitate it completely) with your shoe, this will not stop the roach from walking away. Whilst they do have a brain in their head, much of their nervous system is made up of ganglia located throughout their bodies. What’s more, they don’t need their head to breathe because they do this using little holes called spiracles found on their sides. So, when a headless cockroach dies, it is from thirst, typically a week after you decapitated it with your shoe!
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