As an entomologist, I frequently find myself asked the same few questions by people from all walks of life. In ascending order of frequency, they go something like this:

1. How about those killer bees?

2. What good are mosquitoes, anyway?

3. What good are insects, anyway?

The third question, although by far the most frequently asked, is the most difficult to answer. After all, there are more than a million species and, in theory, there should be more than a million answers. At a rate of one species a day, it would take almost 2,740 years to answer the question properly. Most askers of Question 3, needless to say, aren’t motivated enough to wait around to hear the whole story.

It strikes me, though, as fundamentally unfair that “What good are insects?” is the one question that almost reflexively comes to mind when the discussion turns to insects. After all, ornithologists rarely are called upon to justify the existence of birds; ornithology texts almost never have a section titled “beneficial birds,” whereas virtually every writer of an entomology textbook feels obligated to devote at least a few pages to an apologia for the presence of insects on the planet. One would think that the question “What good are birds?” would be relatively easy to answer, given that there are only about 8600 species of birds in the entire world. But in a way, it’s a more difficult question to answer because, despite their undeniable panache and charm, birds really aren’t all that useful or necessary. If they were all to disappear, life would certainly change. There’d be a little more carrion accumulating, a few species of plants wouldn’t be pollinated, and a few kinds of seeds (like oil palms and mistletoe) wouldn’t get dispersed. Impacts on humans would be subtle, too—some fast food franchises, such as Colonel Sanders Kentucky Fried Chicken, would have to start frying other things, and the number of talking pets in the world would decline precipitously. The world would be undeniably poorer in the absence of bird song and bright color, but life would go on.

So, what would happen if, all of a sudden, all insect life ceased to exist? This question has been asked from time to time by entomologists and, although the time frame varies, the general outcome is usually a matter of agreement—human life as we know it would probably end. Noted entomologist Edward O. Wilson, winner of two Pulitzer Prizes and the National Medal of Science, gives humans about ten years if all invertebrates were to go extinct (with insects constituting the vast majority of invertebrates). In contrast, science fiction writer Charles Pellegrino, in his novel “Dust,” which depicts the catastrophic outcome of a global, pre-programmed extinction of all insect life, gives humans less than six months before the species is reduced to a handful of pitiful survivors in remote outposts scattered throughout the world.

Whatever the time scale, however, bad things would definitely happen to people if insects were to disappear. The value of insects lies not so much in the goods they produce but rather in the services they provide. Honey, wax, shellac, royal jelly, and silk are all very nice but are hardly among life’s necessities. One of the most obvious services insects render, albeit unknowingly, is pollination; this activity invariably headlines the obligatory sections in entomology textbooks detailing the positive aspects of consorting with insects. Because plants for the most part can’t move around, most rely on animal partners to bring males and females together for mating. Insects provide that service (in the form of pollen transport) for a remarkable number of plants, particularly species that have become important to human economies and lifestyles. About one-third of the Western diet results directly from the pollination activities of insects. Among the plants that rely on insect pollinators are such orchard crops as almonds, apples, cherries, citrus fruits, figs, pears, and plums; low-growing fruits such as blackberries, cranberries, melons, raspberries, and strawberries; and vegetables such as asparagus, beans, cabbage, carrots, cucumbers, eggplant, lettuce, peppers, peppers, pumpkins, squash, and tomatoes. Onions, garlic, and hot peppers are also insect-pollinated, the food of the future would be decidedly bland in the absence of insect pollinators. Beverage menus would be impoverished as well, without coffee or tea. Even desserts would be dull in an insect-free world; Theobroma cacao, the tree from which chocolate is made, is utterly dependent on tiny ceratopogonid midges for pollination.

The fact that such forage crops as alfalfa and clover rely on insect pollination affects the human diet indirectly; although most humans don’t eat alfalfa and clover, cattle and sheep do, so without insect pollination supplies of milk, cheese, beef, lamb, and mutton would be greatly reduced. A McDonald’s Big Mac burger in an insect-free world would have no meat, no lettuce, no cheese, no pickle, no onion, and no ketchup; basically, it would be a McBun. Even soy substitutes for meat (tofu hot dogs and soyburgers) would be hard to come by; even though Glycine max, the soybean, doesn’t depend on insect pollination, visitation by bees and other pollinators increases seed set and viability and improves yields.

Our fiber as well as our food needs are met in large part as a result of insect activity. The cotton plant is insect –pollinated, and wool and leather come for the most part from sheep and cattle that have eaten insect-pollinated legumes in their diet. Silk, of course, is a natural fiber produced directly by an insect—Bombyx mori, the Japanese silkworm. As a fiber, it’s remarkable—stronger than steel of comparable dimensions yet elastic and capable of binding brilliantly to dyes. So a world without insects might well be a world with a lot more polyester than we’re accustomed to today.

You might think that the few crop plants remaining that do not rely on insects—mostly members of the grass family such as wheat, rice, and corn, along with coconuts and bananas—might fare better in a world free of insects. That’s not out of the realm of possibility; after all, in the U.S. farmers applied more than 168 million pounds of insecticide to crops in 1997. But those same farmers applied even more herbicide (some 568 million pounds) to their fields than insecticide; weeds are a bigger problem generally than are insect pests. Some of the most noxious weed pests of forage and pasture are in fact controlled largely by insects. Klamath weed, for example, choked off more than 2 million acres of prime northwestern U.S .pasture until two species of chrysomelid leaf beetle were introduced to control the plant, and in Australia some 60 million acres of pasture were freed from the invasive prickly pear by a cactus-eating caterpillar and a few of its fellow travelers. Ragweed, a native North American plant, was accidentally introduced into Europe, along with its highly allergenic wind-dispersed pollen (the main cause of hay fever in the U.S.); it’s now the target of a biological control program involving North American noctuid caterpillars. Although it’s not a certainty, there’s a high likelihood that an insect-free future may be full of hay fever and other allergies caused by the abundance of wind-borne pollen in the air.

Humans might not miss insects in their own diet—they’re vanishingly rare in western cuisines and even where they’re eaten regularly, as mopane worms, termites and locusts are in Africa, gusano de maguey caterpillars and grasshoppers are in Mexico, belastomatid bugs and silkworm pupae are in Asia, and palm weevils and longhorned beetle grubs are in South American, they’re rarely a major component of the diet. But humans are exceptional among the vertebrates in the degree to which we’re independent of insects. Most vertebrates rely heavily on insects in their diet. Approximately 40 to 90% of the diet of freshwater fish consists of insects; trout, salmon, perch, bluegills, sunfish and the like depend on stoneflies, caddisflies, mayflies, midge larvae, and even mosquito larvae (a fact that provides a partial answer to Question 2 posed by so many people). Among the amphibians, frogs, toads, and salamanders depend on insects; about 75% of the diet of the common toad is made up of insects. Among the reptiles, insects are the food of choice for lizards, chameleons, green glass snakes, and horned toads. About one-third of the diet of game birds and songbirds are insects and their relatives; flycatchers, swifts, swallows, woodpeckers, nuthatches, creepers, titmice, some goatsuckers, whipporwills, warblers, vireos, and woodcocks are insect aficionados. The woodpecker-finch of the Galapagos holds a cactus spine in its beak to spear and extricate insects concealed in cavities in dead wood; some shrikes impale their large insect prey on thorns of trees. The quantity of insects consumed by birds is astonishing; nestlings of some species consume their weight in insects on a daily basis. Birds on average consume about a hundred insects a day, but many species beat the average--a flicker was once found with over 5,000 ants in its stomach. And most orders of mammals contain insect-eating species; spiny anteaters, duck-billed platypuses, opossums, cuscuses, caenolestid rat opossums, bandicoots, marsupial moles, hedgehogs, moles, tenrecs, solenodons, shrews, most bats, anteaters, armadillos, pangolins, some mice, and raccoons all consume insects on a regular basis. Even among the primates, our closest relatives, insect-eating is the norm; lemurs, aye-ayes, lorises, tarsiers, marmosets, and several of the great apes are to various degrees entomophagous. Both gorillas and chimpanzees fashion sticks into tools to help them extract termites and ants from their nests.

Admittedly, not all mammals eat insects; those with more omnivorous diets might stand to benefit if insects were to go extinct. It’s unclear what the impact would be of such massive rearrangements of food webs. Among the most omnivorous of mammals are such mammals as rats, who might enjoy untold success in the absence of the insect vectors of diseases that keep their numbers in check. Plague, for example, is hard on humans, having wiped out about one-third of the world’s population in the 14th century, but it’s just as hard on rats, which are also attacked by the flea, Xenopsylla cheopis, that acts as principal vector for the plague bacillus. Plague remains today endemic in western U.S. rodent populations. In the absence of an insect vector, plague would probably decrease in abundance. Rodents are prone to other insect-borne diseases such as tularemia, Chagas’ disease, typhus, and spotted fever. In the absence of insects, rats and their relatives may enjoy world dominance on an unprecedented scale.

If this prospect isn’t bleak enough, there’s still the end of the food chain to consider. Insects are the chief recyclers of the planet and their absence would be marked by accumulating piles of dung and carrion. In the U.S. alone, dung-recycling beetles contribute about $2 billion every year in dung-removal services. Not many other organisms are equipped for this task, which is daunting at the global level, considering that a single cow can produce a dozen cowpats per day, for an annual yield of about 480 kilograms per cow. And it’s not just dung that they process; insects recycle wood in ways unparalleled by other organisms; in Australia, 25% of all dead wood is decomposed by termites. They’re important in conditioning and aerating the soil as well. The great Charles Darwin called earthworms the “intestines of the soil” for their activity in soil processing, but entomologists believe he didn’t give insects their due. Among other things, in many African savannas, where earthworms are conspicuously absent, soil processing is entirely the result of insect activities. Ants, bees, wasps, fly larvae, beetles, crickets, cutworms, cicadas, and (stretching the definition of insects a bit) springtails are soil-dwellers whose comings and goings help keep soil healthy. White grubs can dig down 1.5 m or more, and cicada nymphs burrow down more than 3 meters. As they burrow many insects bring subsoil particles to the surface and carry surface materials down below (like plowing under a cover crop to replenish the soil). They add organic matter to the soil by way of their dead bodies as well as their manure. They are in fact prodigious producers of excrement; in one year in an oak woodland, insect dung contributed over 5% of the nitrogen, 4.5% of the potassium, and 8.2% of the phosphorus returned to the soil.

There are some recycling jobs that no other organisms can handle the way insects can. Dead bodies, for example, are notoriously refractory to processing. Blow flies are among the few species on the planet with collagenase, an enzyme that can break up connective tissue, and clothes moths and dermestid beetles can make keratinase, an enzyme that can decompose the protein that makes up skin, hair, feathers, nails, claws, and fur.

Of course, insects would be missed by scientists, who use them extensively as model organisms to make significant advances. Much of the field of genetics owes its existence to work done on Drosophila melanogaster—the subject of no fewer than four Nobel Prizes. Their small size, cheap diet, and astonishingly rapid rate of reproduction allowed for sophisticated genetic studies that would have cost a fortune and taken years to complete with laboratory rats or guinea pigs. And there would certainly be a few sensitive souls who would feel diminished by the absence of cricket song, firefly flashing, butterfly flitting, and other aesthetic pleasures offered by the class Insecta but these things are difficult to quantify.

So what’s the final picture of a world without insects? Within a decade, would the human race be reduced to a diet of grain and little else, harvested from weed-choked fields on unproductive soil? Will polyester-clad leisure suits chafe as people struggle to keep the burgeoning rat population from taking over their meager fields? Noses dripping from hay fever, gums bleeding from scurvy, and bodies bent from other nutritional deficiencies, would people gingerly step among the dead bodies littering the ground in search of any remaining insects, in the hope of restoring them to their rightful place in the food chain? Probably not—humans are remarkably resourceful and have developed ingenious coping mechanisms before. In Pellegrino’s novel “Dust,” scientists undertake the task of extracting DNA from fossil insects entombed in amber and cloning new insects to replace those that experienced a pre-programmed extinction. But reconstructing an intact organism from fossil DNA is unfortunately only a solution for a science fiction novel—at the moment, it’s beyond the abilities of modern science.

Fortunately, there are much smarter ways to head off disaster, approaches that rely more on attitude and preventative action than on ex post facto molecular biology. Probably the simplest way to insure that the planet keeps functioning in a way that is conducive to human health and happiness is for people to learn to respect the other denizens of the planet, even the small, six-legged ones, and recognize that they’re our partners in preserving the planet and keeping things running the way they’re supposed to. Otherwise, “What good are humans?” becomes a question without a very good answer, at least as far as the rest of the planet is concerned.

May Berenbaum is head of the Department of Entomology at the University of Illinois.