Yes, even tiny insects have brains, though the insect brain doesn't play as important a role as human brains do. In fact, an insect can live for several days without a head, assuming it doesn't lose a lethal amount of hemolymph upon decapitation.
The insect brain resides in the head, located dorsally. It consists of three pairs of lobes. These lobes are fused ganglia, clusters of neurons that process sensory information. Each lobe controls different activities or functions.
The first lobe, called the protocerebrum, connects via nerves to the compound eyes and the ocelli. The protocerebrum controls sight.
The middle lobe, the deutocerebrum, innervates the antennae. Through neural impulses from the antennae, the insect may collect odor and taste cues, tactile sensations, or even environmental information like temperature or humidity.
The third lobe, the tritocerebrum, performs several functions. It connects to the labrum (an insect's movable upper lip) and integrates sensory information from the other two brain lobes. The tritocerebrum also connects the brain to the stomodaeal nervous system, which functions separately to innervate most of the insect's organs.
Other ganglia throughout its body control most of the overt behaviors we observe in insects. Thoracic ganglia control locomotion, and abdominal ganglia control reproduction and other functions of the abdomen. The subesophageal ganglion, just below the brain, controls the mouthparts, salivary glands, and movements of the neck.
The insect brain actually controls only a small subset of functions required for an insect to live. The stomodaeal nervous system and other ganglia can control most body functions independent of the brain.
Read more about the insect nervous system.
- Borror and Delong's Introduction to the Study of Insects, 7th Edition, by Charles A. Triplehorn and Norman F. Johnson
- The Nervous System, John R. Meyer, Department of Entomology, NC State University, accessed 26 October 2010.