Cimex is a genus of insects in the family Cimicidae. Cimex species are ectoparasites that typically feed on the blood of birds and mammals. Cimex lectularius and Cimex hemipterus are known as bed bugs and frequently feed on humans, although other species may parasitize humans opportunistically. Species primarily parasitizing bats are known as bat bugs.

The insects are 3 to 9 millimetres (0.12 to 0.35 in) long and have flattened reddish-brown bodies with small nonfunctional wings.

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