Bed bug is a flat oval shaped insect. They are mostly brown in color. Adult bed bug is about 4 - 5mm long. They have 6 legs and 2 antennas. Bed bug is wingless but the vestiges of wings called wingpad but this does not develop into functional wings. So a bed bug cannot fly. They are about four types of bed bug.
The most common household bedbug is Cimex lectularius. Others types of bed bugs are: Cimetus hemipteius, Cimetus adjunctus and Haematosiphon Inodora. C.hemipteius and C. adjunctus are common in the tropical region. H. inodora is common in North America. After feeding bed bug can swell to about 10 mm and their color change to brown red.