How many insects are there on Earth?

How many insects are there on Earth?

Whether you're talking about a swarm ofbees buzzing about, a cluster ofbutterflies sucking down nectar or a nest of cockroaches hidden in a corner of your house, insects are plentiful. Really plentiful.

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Scientifically speaking, the term "insect" denotes a member of the class Insecta. For brevity's sake, if you have a head, a thorax, an abdomen, three sets of legs protruding from your body and often a pair or two of wings, perhaps for making a quick getaway, then you're most likely an insect. So how many are there?

It seems like an impossible question for good reason: We don't even know how many different insect species there are, which makes it difficult to perform an all-inclusive worldwide insect census, according to David Hogg, an entomology professor at University of Wisconsin-Madison specializing in population ecology and pest management.

Add to that monumental task the often brief life span of an insect, such as the adult mayfly -- a mere 24 hours -- and you'd have some serious difficulty physically counting all the insects filling the planet's air at any given moment [source: Turpin]. If you were really 

interested in this endeavor, you might have more luck counting insect queens of the ant, termite and bee varieties, which may rule their colonies for years. In fact, a termite queen may reign for as long as half a century [source: Turpin].

Of course, entomologists are interested in more than just the ruling class of the insect world, so they've devised automated and old-fashioned ways to survey, count and classify insects present in a select area.

One novel technique for measuring biodiversity may surprise you: A group of scientists sought to find out how many different species of insects inhabited two different regions. To collect the raw data, they used the front bumper of a moving vehicle and the open road. The resulting bug splatter on the bumper contained a treasure trove of genetic evidence from the various insects that struck it. The scientists then sequenced the DNA samples from the splatter and compared it with existing sequence databases for insects [source:Calicchia].

The method isn't perfect, but it does attempt to classify, if not quantify, those buzzing masses.

Counting the World's Insects

The scientists who conducted the experiment described on the last page didn't attempt to collect a sample of every insect species on Earth, but they were able to get a better grasp on the amount of diversity that exists across two separate U.S. regions. And that bumper? It yielded samples from 711 and 1,516 members of the Insecta class in the two regions tested [source: Calicchia].

Globally, scientists have identified about 925,000 species of insects, says Hogg, the entomology professor. Estimates on the number of total insects species fall as high as 30 million and as low as 2 million. The estimate that many people agree upon is about 5 million, so biologists have yet to identify more than 80 percent of the estimated total number of species [source: Hogg]. You can see the complications and uncertainty involved in assigning a number for the total of individual insects out there.

So if you were an entomologist determined to make your mark in the field, a better bet might be to discover a new insect species or two. Where might you look (and be prone to swatting a lot away as you search)? The tropics are the world's most populous places in terms of insects, and tropical environments near the equator are also most conducive to plant and animal diversity [source: Hogg]. Ants are probably Earth's most abundant insect species, says Hogg. In fact, in the tropics, the total biomass (weight) of ants is greater than that of all of the mammals combined.

The United States has insects in great abundance, too. Hogg's research on aphids, an insect species that feeds on soybeans, took him to the Midwest. According to Hogg, in the peak of summer, one soybean plant can house up to 2,000 aphids. One acre can support up to 20,000 soybean plants, and in the upper Midwest, there are close to 40 million acres of soybeans. In other words, that's a lot of aphids -- 1.6 x 1015. But that's just aphids. You came here to learn how many insects there are on Earth, so we're not going to send you away disappointed.

The estimated number of individual insects currently hopping, crawling or flying around our planet at any given moment is about 10 quintillion, or the number "10" followed by 18 zeros, according to entomologist Dr. E.O. Wilson [source: Smithsonian Institute]. That means there are about 2 billion insects for every human being, and assuming that there are 5 million species of insects, that means that each species has about 50 trillion individuals [source: Hogg]. So the next time you feel outnumbered, just remember: Unless you're an insect, so is everyone else.

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