It's no secret why people see more insects than any other animal; they outnumber us by 200 to 1. The name insect comes from the Latin insectum, which means "cut into sections." There are 900,000 known species of insects in the world today, but some scientists believe the species count could be as high as three million.
An insect is an animal that:
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is an invertebrate (does not have a backbone).
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is an arthropod (with an exoskeleton, a segmented body, and paired jointed legs).
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has a chitinous exoskeleton (similar to keratin, which makes up hair, horns, claws, hooves, and the outer layer of human skin)
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has a three-part body (consisting of a head, a thorax, and an abdomen).
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is a hexapod (has three pairs of jointed legs attached to the thorax).
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has two compound eyes (and possibly 3 to 12 simple eyes).
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has one pair of antennae.
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might have one or two pairs of wings.
Although insects have multiple life stages which may not exhibit one or more of the above characteristics, these characterisitics will be present in at least one life stage, usually the adult stage.
In addition, insects:
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are one of the most diverse groups of animals on the planet.
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include over one million known species.
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make up more than half of all known living organisms.
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exist in nearly all environments.
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usually hatch from eggs.
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must molt (shed their exoskeleton) as they grow.
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have three to four stages in their life cycle.
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are the only invertebrates to have evolved flight.
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communicate with chemicals, sounds, or light.
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can damage crops and spread disease.
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are essential to the life cycles of many flowering plants (as pollinators).
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are beneficial predators of harmful organisms.
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provide economic benefit to people (silk, honey, food).
Insect Numbers:
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There are 10 quintillion (10,000,000,000,000,000,000) insects living on the earth right now.
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Coloepotera (beetles) makes up the largest insect order with 23,700 species.
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There are up to 425 million insects on every square acre of land.
Did You Know?
A spider is not an insect because it has a two-part body and eight legs.
With their 3-D vision (called stereopsis), barbed raptorial forelegs, and lightning fast reflexes, praying mantises are expert hunters.
LPhoto by Len Worthington, CC BY-SA 2.0
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The first three pairs of legs on this monarch caterpillar will become the butterfly's legs; the last five pairs (called prolegs) are not present in the adult.
Photo by Katja Schulz, CC BY 2.0
The mason bee (Megachile inermis) sees with two large compound eyes (sides of head) and three small simple eyes, called ocelli (top center of head).
Photo by USGA Bee Inventory and Monitoring Lab, Public Domain
Near its mandibles (jaws), this moth larva (Helicoverpa zea) has six pairs of simple eyes (called stemmata), which can only differentiate between light and dark.Photo by USGA Bee Inventory and Monitoring Lab, Public Domain
The click beetle (Megapenthes limbalis) deploys a unique "click" mechanism to jump out of harm's way.
Photo by Katja Schulz, CC BY 2.0
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