The Bug We Love to Hate
Scorned by city dwellers, the much-maligned cockroach is one of the great success stories of evolution
Behind the U.S. Department of Agriculture laboratory in Gainesville, Florida, sits a tiny house consisting of two kitchens and an attic. Shaded by oaks, framed by Spanish moss dripping from trees, it is an appealing, though somewhat strange, dwelling. Appealing, that is, for entomologist Richard Brenner and the cockroach tenants for which he built it.
The building, custom designed by Brenner, offers its teeming inhabitants all the benefits of a simulated human occupant--including the all-important moisture from, say, cooking spaghetti or bathwater. In the floors, walls, ceilings and roof are 120 sensors to measure humidity, air currents, temperature and cockroach movement. The results go to a central computer, which Brenner, who works with the USDA Medical and Veterinary Entomology Research Laboratory, uses to study how the insects respond to changes in air, light, seasons or availability of food.
This is serious work, with serious consequences: Cockroaches, researchers are finding, not only evoke a visceral "ick" from people, they also can threaten our health. But whatever Brenner discovers about the lives of cockroaches in our homes, his findings will barely scratch the surface of what there is to learn about the insects. For only about 25 of the 4,000 known species worldwide of cockroaches ever intrude on the lives of people. They don't even like us--and have even been known to wash themselves after being touched by people.
Cockroaches come in sizes ranging from ants to mice, in colors ranging from brilliant green to translucent to mahogany. Most species inhabit tropical jungles; many also live in caves, deserts, temperate forests and, of course, every manner of human dwelling--from Manhattan kitchens to the subterranean utility tunnels of Arctic air bases. The nearly flawless (by evolutionary criteria) creatures have been around for 350 million years, since long before the time of the dinosaurs. They can live for vast stretches of time with no food and can withstand massive doses of radiation that would easily kill people. For scientists, then, nearly everything about these bugs is a lesson in survival that goes far deeper than their adaptation to mere human beings.
Cockroaches have been so successful in large part because they are generalists, unlike animals that survive with exquisite adaptations to particular features of their environments. The newer creatures on Earth tend to be the specialists. For instance, lice, only about 75 million years old, evolved in tandem with mammals and birds, which they use as mobile restaurants. Koalas feed solely on certain types of eucalyptus leaves. And pandas eat primarily bamboo. Those strategies can work beautifully--but only as long as the food supply lasts.
Cockroaches, in contrast, are "so generic they can exploit a changing environment," says Richard Brenner. Like their relatives the mantises and grasshoppers, cockroaches have Jack-of-all trades mouths, with working parts evolved from legs. They can chew virtually anything, hard or soft-from algae to dead insects to the metabolite products of the digestion of microbes. Little goes to waste around a cockroach. They eat their own cast-off exoskeletons and they nibble off each other's antennae and legs. After a cockroach brood hatches, the adults apparently eat the embryonic membranes, the egg cases and any unhatched eggs.
"In a home," says Brenner, "they'll eat salts in tennis shoes, bacteria or mold, grease spots on a wall from cooking, the starch on postage stamps and in wallpaper paste-just about anything looks good to them." When they must, cockroaches can survive on virtually nothing. Brenner's laboratory once kept a cockroach colony alive for two and a half years on a diet of no protein at all. Their secret is certain bacteria that live only inside a cockroach organ called the "fat body."
Most insects excrete uric acid. But cockroaches stockpile it for hard times. When a cockroach's diet is rich, the bacteria in its fat body transform the protein's nitrogen into uric acid crystals and store them. When food is scarce, the insect draws upon the stored uric acid for sustenance. When times are really bad, cockroaches sustain themselves on each other. "The strong eat the weak," says Phil Koehler, a University of Florida entomologist who works with the Agriculture Department lab. "They rip off the top of the abdomen and consume the fat body."
Some cockroaches dine inside caves where bats roost, feeding on the moist mounds of guano and bits of fruit and seed the bats rain down, as well as on dead bats. Some cockroach species have dwelled in caves so long they have lost their wings and eyes. In the underground darkness, these bugs seem to set their biological activity clock by the bats' comings and goings, "telling time" by bat-wing-stirred breezes or by the warmth of bat bodies when the night hunters return at dawn.
Scientists speculate that caves were where the bugs first discovered the benefits of living with our ancestors. Later, the insects stowed away aboard Roman and Phoenician galleys to Europe, rode Spanish galleons and slave ships to the Americas, and took rides with traders, migrants and marching armies to go wherever humans have gone.
Cockroaches evolved originally in tropical jungles, where most still live. When entomologist Coby Schal of Rutgers University studied Costa Rican rain-forest cockroaches, he found that every evening, large numbers of adults of some species fly or crawl several meters up into the bushes. At dawn, the bugs sink back into the leaf litter. Schal theorizes the cockroaches ascend to avoid spiders and other nighttime predators of the forest floor, and descend in the morning to escape sight-hunting lizards and birds.
Proof of the cockroaches' versatility is that these insects of humid jungles even colonize deserts, finding moisture in fungi coating desert shrub roots. The bugs' Achilles heel is the speed with which they dry out. So to survive the searing desert day, they move into the moist burrows of tortoises and rodents like the kangaroo rat. (In a range of climates, they also move into nests of bees, wasps, termites, ants and birds.)
If cockroaches are the eating machines, the turbines even, of diners, they are the turbojets of reproducers. The Gainesville lab has determined that in one year a single Asian cockroach (particularly prevalent in Florida) whose young all reproduce will cause 10 million new cockroaches to come into the world. In that same time, under the best possible conditions, a German cockroach (the most ubiquitous urban dweller) can produce more than 500,000 descendants. And many species live as long as four years. "The strategy is to live long and reproduce often," says University of Florida's Phil Koehler.
As far as scientists know, most cockroaches have a few mating tactics in common (with the exception of a North American strain of the species Pycnoscelus surinamensis, which consists only of females and reproduces essentially by cloning). In several species, males perch higher than females. That way, males can smell females' pheromones, or sexual perfume, wafting upwards. A tiny gust of unscented air from below-possibly stirred by a predator-is likely to send a male upward. But at a whiff of female pheromone, it climbs down.
Since the bug's skeleton is external (a hardened carapace called a "cuticle"), mating rituals can appear, to people at least, like undertaking an assignation while clanking around in full armor. Even the bugs' genitalia are an array of hooks and grapples to assure proper positioning.
Consider Gromphadorhina portentosa, the Madagascar hissing cockroach, big as a mouse and aptly named for a noise it makes by pumping air through its breathing holes. The ritual starts with mutual antennae touching (cockroaches taste and smell through chemical sensors on their antennae). Then the male circles the female, hissing and posturing in something of a dance, at the same time releasing a chemical attractant. Stage three, copulation, is an act of engineering. In many species, the male secretes a tasty fluid from his back. When the female clambers up to eat the attractant, she is positioned for the male to attach his grappling hooks. Then the two pivot rear to rear for the transferral of sperm.
The all-important chemicals in these machinations also rule other elements in cockroach lives. An "aggregation" pheromone, for example, draws together German cockroaches, which crowd convivially in dark crevices. The densities and age groups, in turn, are determined by chemicals that broadcast the reproductive state of the females (whether they are ready to mate, pregnant or carrying egg cases).
So much for the more esoteric details of cockroach life. What about the ways these bugs bug us? And how might we rid ourselves of them? First, the bad news: Far from being benign, they are a serious cause of human allergies ranging from tearing eyes to severe wheezing. As much as 60 percent of the 11.5 million Americans who suffer from asthma are allergic to the creatures (whether the insects are alive or long dead--even decades old). In rare cases, some species can also cause vertigo and even potentially fatal anaphylactic shock.
And despite all our human ingenuity, we have not yet found any foolproof ways to control cockroaches. These masters of the art of survival are sure to outlive our own species; we are, after all, a mere blip on their time scale. Cockroaches quickly develop defenses against almost anything we poison them with, probably because they've coped for eons with chemical warfare from plants. "Plants have been putting out anti-insect chemicals since Day One," says biologist Jim Moss, who studies insecticide resistance at the Florida lab.
The good news is that everything scientists are learning about cockroaches holds clues for future ways to deter them. Take the reason desert-dwelling cockroaches seek the kangaroo rat's burrow (for moisture). Richard Brenner has found in his Gainesville laboratory that cockroaches typically spend most of the day backed into a crevice, antennae sticking out, sensitive for air currents. The reason? They must be just as careful of drying out in your home as they are in the desert. One food-deprived cockroach colony in the Gainesville lab died only when a technician forgot to water it over a weekend. "Deny them water and you've hit them hard," says Brenner. So too, he hopes, will the drying action of a new ventilation system he is testing.
The lab's sensors have revealed that cockroaches scurry to cover at the slightest air movement. "We used to think they avoided the light, and that's true, but they also hide away to avoid moving air," says Brenner. (As for avoiding light, anyone who's experienced an invasian of Asian cockroaches can attest that at least one bold species loves illumination--even the glare of a television screen underfoot.)
Until air blowers designed to dry out cockroaches come along, we may be able to thwart the critters with fans at key locations. The experts also recommend general cleanliness and an absence of clutter that can harbor the bugs. As for poisons, anything that will kill a cockroach may also hurt people. "The problem is that we are trying to eliminate something that intimately affects our environment," says Brenner. "The point to our research is learning to very carefully manage the cockroaches' environments without harming people."
A case in point is boric acid (to which cockroaches can't seem to develop resistance-yet!). In powder form, it sticks to the insects, which then ingest it as they clean themselves. Boric acid is best used spread in small amounts where the bugs are likely to tread, but not where it might poison humans. That is easier said than done, however, and carries a risk of toxifying our own environment. Also effective, and far less potentially toxic to people, are baits--which often come as small, black plastic rectangles. The cockroaches actually feed on the poison and then die later.
Those of us who are alarmed by cockroaches may find some perverse consolation in the notion that people provide only a small fraction of the bugs' habitats. The insects might prefer, say, a tree hole to a house. Recalls population biologist Donald Strong of Florida State University in Tallahassee, "The first time I saw a hollow oak cut down, I thought there was a fire inside because the tree hit the ground, split-and black fumes seemed to issue out." The smoke, of course, was cockroaches.
If that image is somehow not soothing, we might learn something from entomologist Harley Rose of Sydney, Australia. Rose maintains that Australia's giant burrowing cockroaches, the length of an adult finger, are ideal pets. And he's not alone. For two years, he has sold about ten mating pairs a month (at $50 a pair). Like the cockroaches that may be benefiting from the steam wafting off your dinner plate, these "cockies" are maintenance free. "You can go away on holidays without any problems about looking after them," says Rose.
Once a New Yorker who shared an apartment with a battalion of cockroaches (headquartered under the bathtub), Richard Wolkomir now lives in Vermont.