Bed bugs are small, wingless insects that have not been known to transmit disease. Adult bed bugs have flat, oval shaped bodies. They are between 1 to 7 millimeters in length (about the size of an apple seed). The size of an adult bed bug varies, because their bodies become larger after a blood meal. After eating they change to a reddish color. Bed bugs are usually active at night and bite humans and animals while they are sleeping. They can live several months without feeding.