Cerci (sing. cercus) are the pair of appendages originating on an insect's abdominal segment 11, which appears as if they are on segment 10. In the most primitive species, the cerci are long and multi-segments and have numerous tactile sensory setae. Cerci are especially useful to soil dwellers because they permit sensory reception when the insect moves backwards. Cockroaches and crickets have special wind receptors on their cerci that detect lunging motions towards them by predators, and these receptors elicit immediate running and evasive action. In the more advanced insects (i.e. the flying insects), the cerci tend to become reduced or lost.

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