There are over 4,000 species of cockroaches. While the word cockroach generally conjures up images of fast critters, scurrying along a kitchen counter, out of these 4,000 species, less than 1% are actually considered pests and inhabit homes. I’m sure you’ll agree with me when I say that’s enough.
So, first off, let’s talk about that small minority. There are 6 species that are pest species and of those, 3 are the ones most encountered. They are the German cockroach, the Oriental cockroach and the American cockroach (all can be found in North America).
The German cockroach is generally considered the worst, mainly because of its size. They are so small that they can easily creep into buildings and are hard to get rid of. These roaches are the reason you hear about cockroaches surviving nuclear blasts and being around when all the rest of the world is destroyed. In the 1960’s, experiments were done with these roaches where they were exposed to more than 5 times the amount of radiation that had resulted from Hiroshima-and survived! Although this is not the same thing as surviving a nuclear blast, it is still impressive. Now imagine someone chasing them around with a little aerosol can. Ha! Yeah, right. These cockroaches are generally thought of as dirty little creatures and while they do groom themselves, they can transport bacteria from places like garbage cans to sanitary places that you wish they wouldn’t, like your kitchen. Because of this, they can spread diseases like food poisoning, dysentery and diarrhea and having large populations of these roaches is thought to contribute to problems like asthma. The German cockroach can also emit secretions that smell like food, in an attempt to attract females, whether or not they are interested in mating.
The Oriental and American cockroaches prefer damp areas-pipes, drainage systems and sewers. The American roaches are the largest of the pests and therefore have a harder time existing in areas where they are easily spotted. There was one study of American cockroaches that found 22 species of bacteria, virus, fungi and protozoa that are known human pathogens, plus 5 species of parasitic worm in field collected animals.
So the thought of cockroaches as dirty, disease spreaders is really not entirely unfounded. But those that are fit into a comparatively small category of a really diverse group of animals and many of those animals play a central role in their ecosystems. So, now I’m going to go over just a little bit of cockroach diversity.
Roaches can range in size from the giant rhinoceros cockroaches (a.k.a. giant burrowing cockroach) from Australia, which are burrowers and are about 8.4 inches, to the teeny tiny wheeler ant cockroaches, which live in leaf-cutter ant nests and are only .1-.2 inches. Some can produce repellent chemicals that can cause temporary blindness or skin rashes.
For example, when annoyed these giant cockroaches emit a substance that make them smell peppery. Some cockroaches make egg cases, that remain attached to the female’s abdomen until she can find a safe place for it (Ensign wasps can deposit eggs into the capsules while still attached to the female. The wasp young will consume the eggs.) Other cockroaches are live bearers.
The Madagascar hissing cockroach is an example. The female will extend the egg case from her body, but then pull it back in to be brooded and the baby roaches come out alive. The parents and young will stay in close contact for long periods afterward. They are also an example of a species that doesn’t have wings, while some other species do. Those that do fly still tend to get around more often by running anyway. Different species of cockroach can run from 2-3 mph. That’s quite impressive, when you take their size into account. And they’re great climbers. This hissing cockroach can even scale smooth glass.
Some types of tropical roaches also use sexual mimicry to outroach a dominant male. When the dominant male opens its wings to attract a female, the impersonator behaves like a female and mounts his competitor. This leaves the dominant male vulnerable and the impersonator will bite the wings off of his opponent, who then scurries away in defeat.
The hissing cockroach has some interesting mating behaviors as well. First off, you might notice that in the image above, the cockroach has two large bumps over what looks like its head (but is actually a protective covering over his head). As you can see below, the males have larger bumps and thicker antennae than the females.
This is because the males will use their horns to fight. The males will ram each other to fight for territory. And of course, these guys get their name from their characteristic hiss. While they’re fighting, the winner seems to hiss more. They hiss by pushing air out of their breathing holes (called spiracles), and they have 4 types of hisses, 3 of which are made only by the males. One type of hiss is to court a potential mate. Another is to defend its territory, which may have several females. It’s a warning to an intruding cockroach. Their hiss also conveys their size and can be used to assess opponents. A third hiss is a battle cry, used when a male disregards its territorial hiss and tries to move in on the harem. And the last hiss is made by all roaches, male and female and signifies annoyance.
These little roaches are great and they can be found in just about any live insect exhibit, often with young roaches crawling around as well. And like the vast majority of cockroaches, they are incredibly important to their ecosystem. But let me explain how.
When you think of the rain forest and all of the beautiful trees, plants, flowers, fruits, shrubs, vines, mosses, etc., it’s easy to assume that the dirt all of this is growing out of is full of nutrients. But it’s not. Most of the nutrients have actually been sucked out of the soil and are in the plants themselves. The dirt has almost none left. That is, until you cue the cockroaches and the other recyclers in the rain forest. They take the dead or decaying trees, plants and organic matter (including poop) and break it all down into basic nutrients again, so that the living plants and trees can take them in. Without roaches and animals like them, these valuable nutrients would be locked away and the rain forest would not be able to sustain itself.
A few species of cockroaches have extra help with their important job. They have a symbiotic relationship with protozoa in their gut that breaks wood down into sugars. Needless to say, they need to pass this helpful organism on from one generation to the next. So, after each molt, the young roaches will eat some of the groups droppings, which will then reinfect them with their helpful partners.
Of course, I appreciate roaches for their important roles. But truthfully, that’s not why I am completely astounded by them. Nope, that is because of their resilience. I have to admire these creatures for their sheer adaptability. I am a fan of the survivors. I mentioned earlier that they can survive radiation poisoning. But that is really just the tip of the ice burg. They have developed immunity to pesticides. They can survive for up to one full month WITHOUT THEIR HEAD!!! Do you remember that going around in a chain e-mail way back when? That is actually a fact. Decapitated roaches continue about their business until they dehydrate. There are a lot of adaptations that make this possible [no blood pressure (won’t bleed to death), breathes through spiracles, which are little holes on its body (like all insects) and has nerve clusters in each body segment, so it can survive without the brain in its head.] It’s so simple and so sophisticated at the same time. It’s like a little recycling machine.
That’s probably why they have been around so long. The largest roach fossil was found in Ohio, in a coal mine, and dated to 300 million years ago. Other than the size, there are only a few tiny details that have changed between fossil roaches and those that are alive today.
On a final note, the geneticist in me insists on pointing out that an observation of the roach Blatella germanica revealed that with a small genetic change, the roach will grow wings on its first thoracic segment, which no modern insect has, but that does appear in some of the earliest winged fossil insects. I know this could be a discussion in itself, but I’ll just leave you to ponder it for now, as this is already a really long post.
And for a little bit of cockroach nostalgia: