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It has long been recognized and documented that insects are the most diverse group of organisms, meaning that the numbers of species of insects are more than any other group. In the world, some 900 thousand different kinds of living insects are known. This representation approximates 80 percent of the world's species. The true figure of living species of insects can only be estimated from present and past studies. Most authorities agree that there are more insect species that have not been described (named by science) than there are insect species that have been previously named. Conservative estimates suggest that this figure is 2 million, but estimates extend to 30 million. In the last decade, much attention has been given to the entomofauna that exists in the canopies of tropical forests of the world. From studies conducted by Terry Erwin of the Smithsonian Institution's Department of Entomology in Latin American forest canopies, the number of living species of insects has been estimated to be 30 million. Insects also probably have the largest biomass of the terrestrial animals. At any time, it is estimated that there are some 10 quintillion (10,000,000,000,000,000,000) individual insects alive.
In the United States, the number of described species is approximately 91,000. The undescribed species of insects in the United States, however, is estimated at some 73,000. The largest numbers of described species in the U.S. fall into four insect Orders: Coleoptera (beetles) at 23,700, Diptera (flies) at 19,600, Hymenoptera (ants, bees, wasps) at 17,500, and Lepidoptera (moths and butterflies) at 11,500.
Several enlightening studies have been conducted involving the numbers of individual insects in a given area. In North Carolina, soil samples to a depth of 5 inches yielded a calculation that there were approximately 124 million animals per acre, of which 90 million were mites, 28 million were springtails, and 4.5 million were other insects. A similar study in Pennsylvania yielded figures of 425 million animals per acre, with 209 million mites, 119 million springtails, and 11 million other arthropods. Even specific insect species have been found to be quite numerous, with calculations of from 3 to 25 million per acre for wireworms (larvae of click beetles).
Certain social insects have large numbers in their nests. An ant nest in Jamaica was calculated to include 630,000 individuals. A South American termite nest was found to have 3 million individuals. Locust swarms are said to hold up to one billion individuals.
These great numbers of insect species and individuals were created by a number of factors including their long geological history, the capability of flight, their small size that allows survival in many various habitats, their ability to store sperm for delayed fertilization, and their general adaptive abilities to the environment. Insects have remarkable fertility and reproductive abilities, which have usually led to the vast numbers of individuals in nature. East African termite queens have been recorded to lay an egg every two seconds, amounting to 43,000 eggs each day. To appreciate the population potentials of insects the example of the housefly is sometimes used, stating that the descendants of one pair of this insect, provided that they all survived during a five month season, would total 190 quintillion individuals.
Recent figures indicate that there are more than 200 million insects for each human on the planet! A recent article in The New York Times claimed that the world holds 300 pounds of insects for every pound of humans.
Selected References:
Erwin, T. L. 1983. Tropical forest canopies: the last biotic frontier. Bulletin of the Entomological Society of America, Volume 29: 14-19.
Janzen, D. 1976. Why are there so many species of insects? Proceedings of XV International Congress of Entomology, 1976: 8494.
May, R. M. 1988. How many species are there on earth? Science, Volume 241: 441-1449.
Pearse, A. S. 1946. Observations on the Microfauna of the Duke Forest. Ecological monographs, Volume 16: 127-150.
Sabrosky, C. W. 1952. How many insects are there? in Insects: The Yearbook of Agriculture. U.S. Dept. of Agr., Washington, D. C.
Prepared by the Department of Systematic Biology, Entomology Section,
National Museum of Natural History, in cooperation with Public Inquiry Services,
Smithsonian Institution
Information Sheet Number 18
