The reason that flies (mosquitoes, horseflies, gnats, etc.) are so hard to catch is their unique wing structure. Most insects have four wings in two pairs. Flies use just their front pair for powering flight. Their back wings have evolved into little, club-shaped structures (halteres). The halteres help stabilize the fly by acting as tiny gyroscopes. If the fly changes its direction or orientation, the vibration of the halteres resists the change, sending information to sense organs at the base of each haltere. The sense organs provide feedback to the muscles that are controlling the wings, allowing for rapid adjustments during flight. The front wings are doing their part too, flapping as fast as 1,000 times per second. A fly has a bulging chest (thorax) to contain the powerful flight muscles. Some flies are even faster, thanks to an adaptation that gets their whole thorax vibrating to power the wings.

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.