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Bug brain

Insects have brains. They may bug us, but insects are capable of complex behaviors and can even learn. For example, leaf-cutting ants collect leaves and use them to farm fungus for food. Honeybees dance to communicate the location of a food source to hivemates. Fruit flies learn to avoid an odor when scientists have previously paired it with an electric shock.

Insect brains are as large as 7.5 millimeters (mm), about one-third of an inch, in diameter. An ant brain is around 0.15mm in diameter but contains some 250,000 nerve cells. A housefly's brain weighs less than half a milligram (about the mass of a fine grain of sand) and has around 350,000 nerve cells. Based on their relative behavioral sophistication, I would estimate that fleas have smaller, less complex brains than ants and flies. At the other end of the scale, a bee's brain contains about 850,000 nerve cells. The human brain has an estimated 100 billion nerve cells.

Two predominant features of the insect brain are optic lobes and mushroom bodies. The optic lobes contain about three-quarters of the nerve cells in a fly's brain. They join the compound eyes and are responsible for filtering and integrating visual information. The mushroom bodies—so called because of their shape—synthesize sensory information, particularly chemical signals, and are largest in bees and other insects with a keen sense of smell. The mushroom bodies may also play a role in memory formation. For example, blocking nerve activity in bees' mushroom bodies with a thin, cold needle prevents bees from learning the association between a novel odor and food.

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