Introducing the Insects

Mantis

Part I

How Many Insects Are There?

When people ask, "How many insects are there?" they usually want answers to two different questions : How many kinds of insects are there? What is the total number of individual insects in the world? An honest answer to both is: Nobody knows exactly.

The number of kinds, or species, is so great that entomologists cannot keep an accurate count, except for small groups. The number of kinds that have already been described and named is estimated by various scientists at 625,000 to 1,500,000. No one can even guess when the big tally will be finished. For such huge groups as beetles and flies, an exact count may never be possible, although generally the numbers of the smaller groups can be tallied more accurately.

Workers in the division of insect identification of the Department of Agriculture estimate that by the end Of 1948 approximately 686,000 different species of insects had been described and named for the entire world. In addition were some 9,000 species of ticks and mites, which are not true insects but look like insects to the lay person.

About two-fifths of the known kinds of insects are beetles. Moths and butterflies, ants, bees, wasps, and true flies comprise another two-fifths.

For North America, north of Mexico, the latest figures show nearly 82,500 kinds of insects, plus 2,613 kinds of ticks and mites. Just as for the world, beetles far outnumber other kinds of insect life, with ants, bees and wasps, and the true flies having a good share. The moths and butterflies, which run second to beetles in the world as a whole, are in fourth place in our area, with 10,300 species. The true bugs are not far behind, with 8,700 species. The remaining 5,400 species belong to the other 19 orders.

Not all 82,500 kinds live in the same locality or even in the same region. The mountains and the plains, the great swamps of the Everglades and peaks of the Sierras, the deserts of the Southwest and the northern forests each has its own particular insects. Some kinds live only on the very top of a mountain or two. Others are found in many States.

From them we can deduce that States of average topography, climate, and vegetation might have 10,000 to 15,000 kinds; there might be fewer species in the smaller States and more in the larger ones that have wide ranges of growing seasons, types of plants, elevation, and so on.

How many insects are injurious to man? Entomologists estimated some years ago that approximately 6,500 species of insects in the United States were important enough to be called public enemies. Today the number is probably closer to 10,000.

How do the numbers of insects compare with those of other animals? In current books on zoology, estimates of the total number of described species of animals range from 823,000 to 1,115,000. If the number of kinds of insects is between 625,000 and 900,000, probably 70 to 80 percent of all the known kinds of animals are insects. That proportion has held quite steady in the estimates of many zoologists for the past century or more.

How many species can we expect to find in any one State? For most States we have no totals. A few tabulations, made in various years, are available:

The starting point of our modern system of naming animals is 1758. In that year the names, pedigrees, and descriptions of all the animals then known were printed in one book of only 824 pages, the Systema Naturae by the great Swedish naturalist, Carolus Linnaeus. He listed 4,379 kinds of animals, of which 1,937 were insects. From that beginning, knowledge has expanded greatly as scientists explored the lesser known parts of the earth from pole to pole and the crannies of the better known places, their own back yards. Within 100 years, nearly 100,000 kinds of insects had been identified. By 1900 the total was about 300,000. It has more than doubled since then. Each year now about 6,000 or 7,000 kinds of insects are described and named for the first time.

Today a mere list of the scientific names of the known insects (based on a conservative estimate of the total number) , without one word of description or anything else, in a book with two columns to a page and print fine enough for 100 lines in each column, would fill a volume of 3,300 pages. To say it in another way: If the names were printed one to a line in an 8-page, 8-column newspaper of average size, without headlines and pictures, more than 8 weeks, including Sundays, would be needed to print only the names of the insects that are already known in the world.

WHAT IS THE REAL TOTAL? So far, we have been considering the number of different species of insects that have been described and named. But how many kinds would there be if all were known and named? No one can say for sure, but the question has provoked a good deal of speculation. Recent guesses vary from 2,500,000 to 10,000,000 different kinds.

Maybe there are not quite so many as some people think, however. For example, a listing in 1949 of the termites of the world recognized 1,717 distinct species, even though some previous estimates ranged as high as 2,600 species. For North America, north of Mexico, there are 41 distinct species, compared to 59 in earlier lists, because further study showed that some proposed names applied only to subspecies or color varieties or were simply synonyms, that is, duplication of names for the same species. That experience in a small and intensively studied group may be repeated to an even greater extent in some of the larger groups. Even so, many really new and hitherto unknown kinds of insects are being found and described every day somewhere in the world, and their number should far exceed any decrease caused by duplication of names. The final roll call may be far short of I million but it seems sure to be somewhere in the millions.

THE NUMBER of individual insects, the second part of our question, is a tremendous problem in itself. No one dares to guess the answer for the world, or a country, or a State. Even for smaller areas, such as acres of square miles, any figures are only approximations based on square-foot samples or similar measures. In any given area, the population of insects will not only depend on such things as the soil and the plants, but it will vary from season to season and even from one minute to the next. Still, samples will give us some ideas of the normal population.