Wondering if insects have brains? Richard Jones explains
Not exactly, says Richard Jones. The insect nervous system has only one brain, but this is not the all-powerful, overriding. singular organ we associate with vertebrate anatomy.
The key to insect structure, and its underlying physiology, is body segmentation.
As insect ancestors evolved, their bodies developed through the duplication of segments, each with its own organs. Over evolutionary time these segments became compressed and fused together, but divisions are still clearly visible in parts of the insect abdomen.
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Inside each segment, sensory and stimulatory nerves radiate from a co-ordinating bundle, called a ganglion, which controls that particular region of the insect’s body, and which can operate on its own. However, the six ganglia in what were once the six front segments, but which are now contained inside a single head capsule, are themselves fused into a single brain.
Controlling the vitally important sensory structures – the eyes, mouthparts and antennae – the brain has assumed dominance over the whole insect, but if decapitated an insect can ‘survive’ for hours or days as an automaton until it starves.
A similar multiplication occurred with the muscular pump that moves the haemolymph (insect blood) through the body cavity.
The modern insect has a series of pumps fused into a tube; this is perforated along its length by ostia (one-way valves) but open at the head end. There are no veins or arteries but, as this organ pumps, hacmolymph passes in through the ostia and is pushed back into the body cavity, creating circulation of sorts.