From Wikipedia:
Nycteribiidae, (superfamily Hippoboscoidea), are known as bat flies, together with their close relatives, the Streblidae. They are flattened, spiderlike flies without eyes or wings, and are seldom encountered by general collectors, as they almost never leave the bodies of their hosts. Both males and females take blood meals. Most species are highly host specific. The family is primarily found in the Old World tropics.