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BzzzzzzzzWhy insects are vital to human survival

By Josie Glausiusz

DISCOVER Vol. 25 No. 06 | June 2004 | Biology & Medicine

‘Something in the insect seems to be alien to the habits, morals, and psychology of this world, as if ithad come from some other planet, more monstrous, more energetic, more insensate, more atrocious,

more infernal than our own.’

— Maurice Maeterlinck, Belgian playwright, 1862-1949

Such animosity hardly seems justified. Of the approximately 9 million species of insectson Earth—the vast majority undiscovered and unnamed—only about 11/2 percent do us

any harm. The rest have either no direct impact or provide some very obvious and

indispensable benefits to humans. They pollinate plants, including 80 percent of the

world’s 94 major food crops, as well as vast tracts of tropical rain forest. Theydecompose our dead and all the waste that animals and plants produce, from dung to

discarded skin, feathers to hair, dead leaves to rotten wood. They protect our harvests by

eating the pests and the weeds that would destroy them. They are food for birds, frogs,reptiles, fish, and mammals—including, wittingly and unwittingly, humans. They aerate

and enrich the soil by digging tunnels and carrying nutrients down from the surface. That,

in turn, helps prevent erosion and runoff into rivers and streams.

MOSQUITO

It isn’t hard to understand why the mosquito is so reviled. Elegant,dainty, and deadly, it is the most common of all blood-sucking

arthropods and the most important insect carrier of human disease,transmitting not only malaria but also yellow fever, dengue, West

Nile virus, encephalitis, and the tiny worms that cause elephantiasis.But mosquitoes, with 3,550 species, have their place in the web of

life. Birds, bats, fish, and many significant wetland species, including



dragonflies, feed on them. Anopheles mosquitoes—among them A.stephensi , shown here—have arguably changed the course of humanhistory. Over the centuries they have killed untold millions with the

aid of the malaria parasite, Plasmodium, which they inject into bloodalong with their saliva. Prior to the widespread use of quinine, infact, it was mosquito-borne malaria that largely protected Africafrom European colonists, who died from the disease in such high

numbers that the west coast of Africa was dubbed the white man’sgrave. Another species, Aedes aegypti , carried yellow fever to theNew World with the African slave trade and helped drive France to

negotiate the Louisiana Purchase in 1803.

If all insects were to suddenly vanish overnight, says Harvard biologist Edward O.

Wilson, it’s likely humans would be endangered. All the plants that insects pollinate

would disappear. All our detritus would pile up to colossal heights. Even the oceanswould be affected. Nutrients would pour down off the increasingly denuded land into the

sea, triggering massive algal blooms, which would exhaust the water of oxygen and

threaten fish. And the impact on terrestrial ecosystems would be enormous. “If insects

were gone, you would break a large part of the terrestrial food chain,” says Wilson. “A

number of birds would starve in no time at all. Those birds and other animals that dependon birds for food would disappear. Small mammals in the soil that depend, in part, on

insects would disappear. It would be a catastrophic chain reaction around the world.”

No one expects insects to evaporate into the ether, of course. But if insects had not

evolved, humans probably wouldn’t exist either. That’s because the flowering plants on

which we ultimately rely for nearly all our food came into dominance along with winged

insects just after the extinction of the dinosaurs 65 million years ago. “A large portion of the flowering plants, or angiosperms, depended on the insects for pollination, and insects

were a major factor in creating the soil conditions on which the plants grew,” Wilson

says. “Humans came out of mammals, and mammals came out of vertebrates that were

totally dependent on the flowering plants—grasslands and forests and so on. If insectshad never originated, I’d say there’s virtually no chance that humans would have evolved

as we know them. If an intelligent creature had evolved, it would probably not have beenhumanlike.”

Insects are far less dependent on us than we are on them. There is, however, a small

subset of insects that would probably not exist, in their present form or state of

superabundance, if humans did not provide them with a ready food supply. Theuniversally despised cockroach, for example, has followed humans (and their trail of

crumbs) to the ends of the earth and beyond: One was even spotted scurrying around on

the Apollo XII spacecraft. The females of as many as 85 species of Anopheles mosquito

suck human blood in order to nurture their eggs, often transmitting the protozoan malaria parasite, Plasmodium, in the process. Body lice, Pediculus humanus corporis, probably

took up residence in garments only after humans began wearing them around 72,000

years ago, while their relatives Phthirus pubis, crab lice, live among human pubic hairsand rarely anywhere else. The common bedbug Cimex lectularius —known as “the sex

maniac of the insect world” for its insatiable lust—probably evolved in caves as a

parasite of bats or birds before it began feeding on human blood. Other insects, such aslocusts, granary weevils, and aphids, found a profitable niche when humans invented

agriculture 10,000 years ago and grain storage some 5,500 years later. And houseflies,

carpet beetles, silverfish, and various species of moths and fleas have all set up homewith humans.



At the same time, we have exploited insects—for honey, beeswax, silk, and various,

usually dubious, forms of medicine. We have also seen them as a source of inspiration:

The Egyptians symbolized their sun god, Ra, as a great scarab beetle rolling the sun like a ball of dung across the heavens. Even the much-detested mosquito is held up as an

example in the Talmud. “Why was the mosquito created before man?” it asks. “So that if

man becomes haughty, he can be deflated by being told, ‘The mosquito came beforeyou.’”

Insects—which, like humans, make music, communicate in symbols, grow subterranean

crops, enslave each other, and even fight wars—have also stirred the human imagination,

giving rise to everything from the band name The Beatles to Franz Kafka’s immortal heroGregor Samsa, who awakes one morning to find himself transformed in his bed into a

gigantic insect. Instead of reaching for the bug spray, then, why not celebrate our bond

with insects? As the venerable Jules Michelet wrote in his 1858 epic, The Insect , “We aretruly somewhat akin. For what am I myself, but a worker? What has been my greatest

happiness in this world?”

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