Bed bugs are parasitic insects of the Cimicid family that feed exclusively on blood. Cimex lectularius, the common bed bug, is the best known as it prefers to feed on human blood.
Adult bed bugs are light brown to reddish-brown, flat, oval-shaped, and have no hind wings. The front wings are vestigial and reduced to pad-like structures. Bed bugs have segmented abdomens with microscopic hairs that give them a banded appearance. Adults grow to 4–5 mm (0.16–0.20 in) long and 1.5–3 mm (0.059–0.118 in) wide.
Newly hatched nymphs are translucent, lighter in color, and become browner as they moult and reach maturity. A bed bug nymph of any age that has just consumed a blood meal has a bright red, translucent abdomen, fading to brown over the next several hours, and to opaque black within two days as the insect digests its meal. Bed bugs may be mistaken for other insects, such as booklice, small cockroaches, or carpet beetles; however, when warm and active, their movements are more ant-like and, like most other true bugs, they emit a characteristic disagreeable odor when crushed.
Bed bugs use pheromones and kairomones to communicate regarding nesting locations, feeding, and reproduction.
The lifespan of bed bugs varies by species and is also dependent on feeding.
Bed bugs can survive a wide range of temperatures and atmospheric compositions, below 16.1 °C. Adult bed bugs enter semi-hibernation and can survive longer; they can survive for at least five days at −10 °C, but die after 15 minutes of exposure to −32 °C. Common commercial and residential freezers reach temperatures low enough to kill most life stages of bed bug, with 95% mortality after 3 days at −12 °C. They show high desiccation tolerance, surviving low humidity and a 35–40 °C range even with loss of one-third of body weight; earlier life stages are more susceptible to drying out than later ones.