National Geographic : 1981 Jan
viruses shelter in cockroaches as do the eggs of parasitic worms. Remarkably, cockroaches have never been conclusively linked to epidemics of human disease. And unsavory microbial companions aside, the insects are fussy. They groom themselves as diligently as cats, brushing cerci with spiny hind legs, combing antennae, and rubbing against sol id objects as horses rub against fence posts to scrape dust and dirt off their backs. Their fastidiousness preserves the epicuticle, a vulnerable coating of wax and oils that pre vents a cockroach from drying out. Such a varnish is vital to species like the American roach, 75 percent water by weight. Abrade too much of this waterproofing, and within hours the insect withers away. Some householders exploit this Achilles' heel by scattering diatomaceous earth-the chalky, sharp-edged shells of one-celled water plants-where roaches are most likely to pick up the abrasive dust. Powdered boric acid, the stuff of eyewash, has the same ef fect, and is poisonous to roaches as well. While not as potent as synthetic insecticides, these cheap dusts are longer lasting and less repellent to the cockroach, an insect that learns to shun some chemical poisons before picking up a lethal dose. Termites are more destructive, rats more dangerous, but cockroaches are an extermi nator's bread and butter, worth half a billion dollars yearly in repeat business. Egalitar ians, the pests afflict rich and poor alike, and do-it-yourselfers annually strike back with another 150 million dollars' worth of dusts, sprays, and baited traps. Caught in a chemical barrage, roaches have become resistant to many once deadly The enduring world of cockroaches counts such exotic citizens as Neostylo pyga rhombifolia (above), the harle quin roach, of Central America. The four-inch-long Blaberus giganteus (left) of Central and South America reignsas one of the largestroaches.