I asked some friends what words come to mind when I say "cockroach." Their answers typified how most people feel about roaches: "stomp," "ewww," and "Joe's Apartment!" I'm here to tell you that cockroaches are not all that bad. In fact, they're rather cool. Here are 10 facts about cockroaches that might persuade you to think differently about these insects.
1. The vast majority of cockroaches are not pests.
What image do you conjure up when you hear the word cockroach? For most people, it's a dark, dirty city apartment teeming with cockroaches. In truth, very few cockroach species inhabit human dwellings. We know of some 4,000 species of cockroaches on the planet, but only about 30 of these can be considered pests. Most cockroaches inhabit niche habitats in forests, caves, burrows, or brush.
2. Cockroaches can eat just about anything, and can survive without food for long periods of time.
Cockroaches are scavengers. While most roaches prefer sweets given a choice, in a pinch, they will eat just about anything: glue, grease, soap, wallpaper paste, leather, bookbindings, or even hair. Worse yet, a cockroach can survive a remarkably long time without food. Some species can go as long as 6 weeks without a meal! These traits make cockroaches in our homes tough to control. But in nature, cockroaches provide an important service by consuming organic waste. They're the garbage collectors of their habitat.
3. Roaches have walked the Earth for hundreds of millions of years.
If you could travel back to the Jurassic Period and walk among the dinosaurs, you would easily recognize the cockroaches crawling under logs and stones in prehistoric forests. The modern cockroach first came to be about 200 million years ago. Primitive, ancestral roaches appeared even earlier, about 350 million years ago, during the Carboniferous Period. The fossil record shows that Paleozoic roaches had an external ovipositor, a trait that disappeared during the Mesozoic Era.
4. Cockroaches like to be touched.
Roaches are thigmotropic, meaning they like feeling something solid in contact with their bodies, preferably on all sides. They seek out cracks and crevices, and will squeeze into spaces that offer them the comfort of a tight fit. And I do mean a tight fit. The small German cockroach can fit into a crack as thin as a dime, while the larger American cockroach will squeeze into a space no thicker than a quarter. Even a pregnant female can manage a crevice as thin as two stacked nickels.
5. Cockroaches incubate their eggs in sacs or capsules called oothecae.
Mama cockroach protects her eggs by enveloping them in a thick protective case, called an ootheca. German cockroaches may encase as many as 40 eggs in one ootheca, while the larger American roaches average about 14 eggs per capsule. A female cockroach can produce multiple egg cases over her lifetime. In some species, the mother will carry the ootheca with her until the eggs are ready to hatch. In others, the female will drop the ootheca, or attach it to a substrate.
6. Cockroaches get their vitamins from bacteria that live in their bodies.
For millions of years, cockroaches have carried on a symbiotic relationship with special bacteroides carried within their own bodies. The bacteroides live within special cells called mycetocytes, and are passed down to new generations of cockroaches by their mothers. In exchange for living a life of relative comfort inside the cockroach's fatty tissue, the bacteroides manufacture all the vitamins and amino acids the cockroach needs to live. This arrangement allows the cockroach to dine on just about anything it finds, without concern for its lack of nutritional value.
7. Cockroaches can live for weeks without their heads.
As crazy as this sounds, entomologists have actually decapitated roaches to study this phenomena. Lop the head off a roach, and a week or two later it will still respond to stimuli by wiggling its legs. Why? Because the head of a roach isn't all that important to how it functions. Cockroaches have open circulatory systems, so as long as the wound clots normally, they aren't prone to bleeding out. Their respiration occurs via spiracles along the sides of the body. And they can survive without eating for weeks. Eventually, the cockroach will either dehydrate or succumb to mold.
8. Cockroaches are fast!
Anyone who shares their home with cockroaches will tell you how fast they scurry for cover when you flip on the light switch. But when I say they're fast, I mean measurably fast. Cockroaches detect approaching threats by sensing changes in air currents. The fastest start time clocked by a cockroach was just 8.2 milliseconds after it sensed a puff of air on its rear end. Once all six legs are in motion, a cockroach can sprint at speeds of 80 centimeters per second. And they're elusive, too, with the ability to turn on a dime while in full stride.
9. Cockroaches in the tropics are big.
If a cockroach is in your kitchen, you probably think it's big. But consider yourself lucky, because most domestic roaches don't come close to the size of their giant, tropical cousins. Megaloblatta longipennis boasts a wingspan of 18 cm, or 7 inches. The Australian rhinoceros cockroach (Macropanesthia rhinoceros) weighs a hefty 33.5 grams. The giant cave cricket, Blaberus giganteus, measures 4 inches long at maturity. Aren't you glad these cockroaches aren't running around on your kitchen counters?
10. Cockroaches can be conditioned, just like Pavlov's dogs.
Russian physiologist Ivan Pavlov first documented the concept of classical conditioning, famously demonstrated by his salivating dogs. The dogs would hear a ticking metronome each time they were fed. Soon, the sound of the metronome alone was enough to make the dogs salivate in anticipation of a meal. Makoto Mizunami and his colleague Hidehiro Watanabe, both of Tohoku University, found cockroaches could also be conditioned this way. They introduced the scent of vanilla or peppermint just before giving the roaches a sugary treat. Eventually, the cockroaches would drool – yes, drool – when their antennae detected one of these scents in the air.