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Nycteribiidae is a family of the true fly superfamily Hippoboscoidea are known as "bat flies", together with their close relatives the Streblidae. As the latter do not seem to be a monophyletic group, it is conceivable not to unite all bat flies in a single family.
They are flattened, spiderlike flies without eyes or wings, and as such bear very little resemblance to other Dipterans. These flies are seldom encountered by general collectors, as they almost never leave the bodies of their hosts. Both males and females take blood meals, thus they qualify as real parasites. Most species are highly host-specific. The family is primarily found in the Old World tropics; a few of the 274 known species occur in the Neotropics and in Europe.
One of the key morphological features of Nycteribiidae is their highly reduced compound eyes. Many species of Nycteribiidae contain no visible eyes or contain only rudimentary eye spots. None of the species contain wings. They have backward folded legs that resemble those of spiders and a dorsally inserted head.