The Importance of Insects in the Web of Life

From feeding flesh eaters to plant reproduction, the essential role bugs play in the survival of many ecosystems is hard to overstate. In this article, learn more about the astounding importance of insects.


| May 3, 2012



How-Not-To-Be-Eaten

All animals must eat. But who eats who, and why, or why not? Because insects outnumber and collectively outweigh all other animals combined, they comprise the largest amount of animal food available for potential consumption. How do they avoid being eaten? “How Not to Be Eaten: The Insects Fight Back” reveals the ingenious methods insects employ to stay alive.


COVER: UNIVERSITY OF CALIFORNIA PRESS

From masterful disguises to physical and chemical lures and traps, predatory insects have devised ingenious and bizarre methods of finding food. Equally ingenious are the means of hiding, mimicry, escape and defense waged by prospective prey in order to stay alive. In How Not to Be Eaten: The Insects Fight Back (University of California Press, 2012), Gilbert Waldbauer conveys an essential understanding of the unrelenting coevolutionary forces at work in the world around us by revealing and explaining the importance of insects. The following is an excerpt from Chapter 1, “Insects in the Web of Life.” 

Insects constitute by far the largest amount of animal food available to flesh eaters both on dry land and in freshwater. The one quarter of the earth that is not covered by the oceans and seas is inhabited by an immense and not yet completely censused population of insects. The 900,000 currently known insect species (at least three million are yet to be discovered and named, according to reasonable estimates [Stephen Marshall]) constitute about 75 percent of the currently known 1,200,000 animal species on land, in freshwater, and in the oceans. The Canadian entomologist Brian Hocking made the daring but educated guess that the world population of insects is about one quintillion (1 followed by eighteen zeroes) individuals. Even if he overestimated by trillions, that would still be a stupendous population.

Although insects are small, they are generally so numerous in most terrestrial and freshwater ecosystems that, on a per-acre basis, they not only outnumber but also outweigh all the other animals—including deer and moose—combined. On the face of it, this is hard to believe. But keep in mind that a single acre of land may be home to many millions of insects of hundreds or even thousands of species. By contrast, the home territory of one small bird is likely to encompass as much as an acre, and that of a large mammal, such as a thousand-pound moose, several hundred or even thousand acres. Thus the biomass of an animal that weighs hundreds of pounds may be much less than one pound per acre. Also keep in mind that most people notice only a few of the many insects around them, perhaps a ladybird beetle or a large and beautiful butterfly, but more often the insects that sting, bite, or otherwise annoy them. Yet the other insects, by far the vast majority in almost any ecosystem, go unnoticed. Not only are they small, but many are difficult to see because they are camouflaged, and many are out of sight because they live in the roots, stems, or other parts of plants; as parasites within the bodies of insects and many other animals; or in the soil or other cracks and crevices of the environment.

Insects are, either directly or indirectly, the most plentiful source of flesh for animals that don’t eat plants. But they are important to these predators not just because of their abundance. Plant-feeding insects, estimated to be about 450,000 species, and the insects and other animals that eat them are by far the most important link between green plants and animals that don’t eat plants, a conduit through which predators receive the energy of the sun, which green plants—and only green plants—can capture and make available to animals via photosynthesis, in the form of sugars. Insect-eating insects play another significant, although less important, role. By eating tiny organisms and incorporating their prey’s nutrients in their own bodies, large insects become “nutrient packages” for large insectivores that cannot profitably pursue and eat tiny organisms themselves.

Data gathered by Eugene Odum and other ecologists show just how important a part of the food chain insects are in specific ecosystems. For example, in a field of herbaceous plants in North Carolina, the biomass of the plant-feeding insects alone—not including any predaceous, parasitic, or scavenging species—was nine times greater than that of sparrows and mice, the larger and more conspicuous and by far the most numerous of the vertebrates in that field. On an East African plain, just two species of ants—only those two, among hundreds of other kinds of insects—were about equal in weight, per acre, to the combined weight of the large grazing animals, such as wildebeests, zebras, and antelopes. In these two habitats and in almost all others, insects are by far the most abundant of the prey animals in both numbers and biomass. As is to be expected, and as we will see in the next chapter, hundreds of thousands of different kinds of animals exploit this nutritious, protein-rich food: spiders, scorpions, insects, frogs, toads, lizards, birds, mammals.

The insects almost certainly have more different lifestyles, ways of surviving and “making a living,” than do any other group of animals. One species or another occupies every—or nearly every—ecological niche. An ecological niche is not just a place; it includes all of the resources, food, nesting sites, hiding places, and so on, required by an organism. Except for aquatic species, insects that undergo gradual metamorphosis occupy essentially the same niche throughout their lives. Those with complete metamorphosis often occupy two very different niches in their larval and adult stages.





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