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.

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.