Do Insects Have Brains?

They are smart and have a considerable ability to memorize

Insects do have brains, as noted in this illustration.
Insects do have brains. The insect brain is located dorsally in the head, as seen in this illustration. Illustration courtesy of Piotr Jaworski (Creative Commons license), modified by Debbie Hadley

Even tiny insects have brains, though the insect brain does not play as important a role as human brains do. In fact, an insect can live for several days without a head, assuming it does not lose a lethal amount of hemolymph, the insect equivalent of blood, upon decapitation.

The Three Lobes of the Insect Brain

The insect brain resides in the head, located dorsally, or to the back. It consists of three pairs of lobes: the protocerebrum, the deutocerebrum, and the tritocerebrum. These lobes are fused ganglia, clusters of neurons that process sensory information. Each lobe controls different activities or functions. Neurons vary in number among insect brains. The common fruit fly has 100,000 neurons, while a honeybee has 1 million neurons.

The first lobe, called the protocerebrum, connects via nerves to the compound eyes and the ocelli, which are light-sensing organs that detect movement, and controls sight. The protocerebrum contains the mushroom bodies, two bunches of neurons that make up a significant part of the insect brain.

These mushroom bodies comprise three regions: the calices, the peduncle, and the alpha and beta lobes. The neurons here are called the Kenyon cells. The calices serve as the input areas, where external stimuli are received; the peduncle is the transfer region; and the alpha and beta lobes are the output region.

The middle of the three main brain lobes, the deutocerebrum, innervates the antennae, or supplies them with nerves. Through neural impulses from the antennae, the insect may collect odor and taste cues, tactile sensations, or even environmental information such as temperature and humidity.

The third main 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.

Insect Intelligence

Insects are smart and have a considerable ability to memorize. There is a strong correlation between mushroom body size and memory in many insects as well as between size of the mushroom bodies and behavioral complexity.

The reason for this attribute is the Kenyon cells’ remarkable plasticity: They will readily rebuild the neural fibers, acting as a sort of neural substrate on which new memories can grow.

Functions Not Controlled by the Insect Brain

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.

Various ganglia throughout the 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 mouth parts, salivary glands, and movements of the neck.

Sources:

  • 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
  • bioteaching.com, http://bioteaching.com/insect-brains-and-animal-intelligence/