If you've heard a chorus of crickets, you know that orthopterans make sound. Males make nearly all the sounds, to defend territories and attract females. Specialized body parts are rubbed together (stridulation) to produce the sound. Male grasshoppers, for example, rub hard edges (scrapers) of their hind legs against rows of tooth-like bumps (files) on their front wings. Male crickets chafe their front wings together, also causing files to rub scrapers. Females detect the sounds with ears on their front legs or their abdomens. Like car speakers that blast loud music, natural amplifiers have evolved as orthopteran males try to outcompete each other. The amplifier may be a body part, such as a shield-like plate that reflects sound (in katydids), or a part of the environment, such as a burrow used by singing crickets. Older males are at a disadvantage, at least in some species, because their worn-down files do not make as loud a sound.

Insects are by far the most diverse and abundant group of organisms on Earth. More than one million insect species have been identified, and estimates of how many species exist range into the tens of millions. Insects got their start way back, in the Paleozoic (about 500 million years ago) and have evolved in tandem with flowers (coevolution). Insects have become specialized on particular flowers, leading to complex sets of adaptations that couple them in a feeding and pollination relationship (a mutualism). Specialization allows for many types of insects to live in the same habitat, accommodating their exceptional biodiversity. In a backyard in the temperate zone, one might find several thousand species of insects. Specialization can occur within one plant species as well, with different insects using different parts of the plant. In just one species of tropical tree, Dr. Terry Erwin of Smithsonian's National Museum of Natural History found about a thousand species of beetles.