Nobody wants to see a cockroach scurrying under the fridge when flipping on the light switch. These creatures aren't exactly revered. Entomologists know otherwise, though; these insects are actually rather cool. Here are 10 fascinating facts about cockroaches that just might persuade you to think differently about them.

1. Most Species 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, most of which inhabit forests, caves, burrows, or brush. Only about 30 species like to live where people do. In the U.S., the two most common species are the German cockroach, known as Blattella germanica, and the American cockroach, Periplaneta americana.

2. Cockroaches Are Scavengers

Most roaches prefer sugar and other sweets, but they will eat just about anything: glue, grease, soap, wallpaper paste, leather, bookbindings, even hair. And cockroaches can survive a remarkably long time without food. Some species can go as long as six weeks without a meal. In nature, cockroaches provide an important service by consuming organic waste. As with houseflies, when cockroaches take up residence among humans, they can become vehicles for spreading diseases as they scuttle about the home. Feeding on waste, trash, and food, they leave germs and droppings in their wake.

3. They've Been Around For a Long Time

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 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, squeezing into spaces that offer them the comfort of 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. Cockroaches are also social creatures, preferring to live in multigenerational nests that can range from a few bugs to several dozen. In fact, according to research, cockroaches that don't share the company of others can become ill or unable to mate.

5. They Lay Eggs, Lots of Them

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. Roaches Love Bacteria

For millions of years, cockroaches have carried on a symbiotic relationship with special bacteria called Bacteroides. These bacteria 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.

7. Cockroaches Don't Need Heads to Survive

Lop the head off a roach, and a week or two later it will still respond to stimuli by wiggling its legs. Why? Surprisingly, its head isn't all that important to how a cockroach 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. Eventually, the headless cockroach will either dehydrate or succumb to mold.

8. They're 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, or about 1.7 miles per hour. And they're elusive, too, with the ability to turn on a dime while in full stride.

9. Tropical Roaches Are Big

Most domestic roaches don't come close to the size of their giant, tropical cousins. Megaloblatta longipennis boasts a wingspan of 7 inches. The Australian rhinoceros cockroach, Macropanesthia rhinoceros, measures about 3 inches and can weigh 1 ounce or more. The giant cave cricket, Blaberus giganteus, is even larger, reaching 4 inches at maturity.

10. Cockroaches Can Be Trained

Makoto Mizunami and Hidehiro Watanabe, two scientists at Japan's Tohoku University, found cockroaches could be conditioned much like dogs. They introduced the scent of vanilla or peppermint just before giving the roaches a sugary treat. Eventually, the cockroaches would drool when their antennae detected one of these scents in the air.

More Crazy Cockroach Facts

It's often been said that cockroaches are so hardy that they can survive a nuclear explosion. Although the bugs can survive levels of radiation that would kill a human being within minutes, higher levels of exposure can be deadly. In one experiment, cockroaches were exposed to 10,000 rads of radiation, about the same amount as the nuclear bombs dropped on Japan during World War II. Only about 10 percent of the test subjects survived.

These hardly bugs can also hold their breath for 4 to 7 minutes at a time. Scientists aren't sure why cockroaches do this, but researchers in Australia say it may be in order to preserve moisture in dry climates. They can also survive for several minutes under water, though exposure to hot water can kill them.

Sources: