While their stings are painful or even dangerous, we depend on hymenopterans for our survival. Bees are the main pollinators of the flowering plants that provide most of the world's food supply. Bee adaptations, such as hairy bodies and legs, have evolved for easy pollen collection. Other hymenopterans, such as wasps, are predators that kill insects and spiders. Some hymenopterans are parasites, laying eggs on other "host" insects, which may eventually die from the feeding larvae that hatch out. We benefit from predatory and parasitic hymenopterans that target the many insects that would otherwise be eating crops. Many hymenopterans are social, living in large colonies of related individuals, headed by a queen. Social insects procure their food cooperatively, and humans profit from the way honeybees collect and process flower nectar into honey. The sophisticated chemical senses of hymenopterans support the behaviors, such as nectar collection and pollination, that benefit us.

An insect has a brain, connected to bundles of nerves (ganglia) in each of its three body segments. Like us, they have sensory nerves that receive information from their environment and send it to the brain. Information comes from many types of touch receptors. Touch-sensitive hairs all over an insect's body are sensitive enough to detect vibrations in the air, such as from an approaching predator. Insect hairs also do chemical detection (chemoreception). Pores at the end of chemoreceptors on mouthparts or other body parts allow odors to reach the nervous system. Insect antennae may have thousands of chemoreceptors, used to detect chemicals in the air (pheromones) emitted by members of the opposite sex. An insect, like us, has a pair of eyes on its head. But, insect eyes are compound, with hundreds or thousands of lenses, together making an image consisting of spots of light, like pixels. An insect's sound receptors are on its legs.

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.