True bugs are diverse, ranging from tiny lace bugs to large water boatman. Their diets are diverse as well, but all true bugs feed by piercing and sucking food. The beak-like mouthpart of a true bug is like a trough that folds back under its body. One channel of the trough sends saliva out to moisten food, while the other channel sucks liquid food in. Despite their similar feeding apparatuses, the diets of true bugs vary. Many feed on sap, sucking it out of leaves, flowers, stems, shoots, or roots. Others are predators, using sharp beaks to stab small prey such as snails. Parasitic true bugs, such as bed bugs, pierce the skin of mammals or birds and feed on their blood. More unusual diets include jellyfish or fungi from under tree bark. The piercing and sucking technique even allows some true bugs to liquefy and eat mosses or seeds.

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.