Section 1


• Relate the major characteristics of insects to insects' biological success.

• List both harmful and beneficial effects of insects on human society.

• Describe the external structure and organ systems of a grasshopper.

• Compare incomplete and complete metamorphosis in insects.

• Describe defensive adaptations in insects.

vocabulary entomology labrum labium tympanum ovipositor metamorphosis incomplete metamorphosis nymph complete metamorphosis pupa figure 37-1

The African goliath beetle (a) and Atlas moth (b) are among Earth's largest insects.

figure 37-1

The African goliath beetle (a) and Atlas moth (b) are among Earth's largest insects.

Careers in BIOLOGY


Job Description Entomologists are scientists who study insects and other terrestrial arthropods. Studying insects can be exciting because insects make up more than half of all animal species. Some entomologists research the classification, distribution, or physiology of insects. Some work in medicine and agriculture to reduce insect pests that spread disease or to use beneficial insects to control harmful pests. Entomologists may work in universities, museums, private companies, or government agencies.

Focus on an Entomologist

"You look for beauty in the small," says entomologist and professor Genaro Lopez. Lopez and his students are performing field surveys of pseudoscorpions. "My students can be world experts if they continue to study them for another year or two!" notes López. López enjoys telling stories about scorpions, butterflies, drag-onflies, and other insects, to capture his biology students' attention. López specialized in entomology for several reasons. "I wanted to study an entire animal—and, I wanted to be outdoors," says López. He also likes studying insects because they play roles that are important to humans.

Education and Skills

• High school—three years of science courses and four years of math courses.

• College—bachelor of science (B.S.) in biology, including course work in

ecology, botany, and zoology; for research, a master's degree (M.S.) or doctoral degree (Ph.D.) is needed.

• Skills—attention to detail, self-motivation, curiosity, patience, ability to work independently, fitness, and survival skills.

For more about careers, visit and type in the keyword HM6 Careers.

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For more about careers, visit and type in the keyword HM6 Careers.

The study of insects and other terrestrial arthropods is called entomology (ENT-uh-MAHL-uh-jee), and the scientists who engage in it are known as entomologists. Entomologists classify insects into more than 25 orders based on characteristics such as the structure of mouthparts, number of wings, and type of development. Several of the more common insect orders are listed in Table 37-1.

The Success of Insects

Insects live almost everywhere in the world except in salt water. Entomologists have described and classified nearly 1 million insect species, or more species than exist in all other animal groups combined. In terms of their widespread distribution and great abundance, insects are very successful.

One of the most important factors responsible for the remarkable success of insects is their ability to fly, which enables them to escape from predators and disperse rapidly into new environments. Like other arthropods, insects also benefit from having a light but sturdy exoskeleton and jointed appendages that perform a variety of functions. In addition, most insects are small, so several species can inhabit different local environments within an area without competing with one another for food or other resources. Finally, insects generally have very short life spans and produce large numbers of eggs. Therefore, natural selection can occur more quickly in insects than in organisms that take longer to reach maturity.

TABLE 37-1 Common Insect Orders


(meaning of order name)

Approximate number of species


Type of metamorphosis


Significance to humans


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