Bed Bug Identification

bed bug anatomy
Cimex lectularius (Common bed bug)



Adult bed bugs are generally 3/16″ long by about half as wide. They range in color from mahogany to dark brown. They have a 3 segmented body: head, pronotum, and abdomen. The head has two knob-like protrusions on each side of the head that are the eyes. Just in front of the eyes, there’s two antennae. The antennae are 4 segmented, with the first two segments closest to the head noticeably thicker than the last two segments. Behind the head is the pronotum. The pronotum is a concave-shaped structure that envelopes the head in a wing-like fashion. Behind the pronotum are two wing pads, absent of wings. Bed bugs do not fly.  The last segment is the abdomen. It ‘s an 11-segmented section that contains “hunger folds” on segments 2 & 5. These hunger folds allow bed bugs to take in large blood meals and “balloon” as they feed. The body of the adult bed bug is sclerotized or “leatherly” in appearance and to the touch.




Immature life stages of bed bugs are referred to as nymphs. Depending on their age & development, they’re classified as 1st, 2nd, 3rd, 4th or 5th “instars”. Early stage nymphs can be the size of a poppy seed, while later stages can be any size up to the adult’s typical; 3/16″. Nymphs vary in a number of ways from adults. First, nymphs can appear as either straw colored or almost clear. This is especially true for early instar nymphs. When a 1st instar nymph emerges from it’s egg, it’s completely void of color. The insect takes on color after feeding for the first time, literally filling its internal organs with blood. As a result, it’s easy to see the internal organs of 1st & 2nd instar nymphs. As the insect approaches the 3rd and 4th instar, the entire body darkens to a crimson red. Fourth and 5th instars begin to assume the color of adults, ranging from mahogany to dark brown. Other differences in nymphs include: lack reproductive structures, lack of a sclerotized or leathery bodies, and they posses only a 2-segmented tarsus (foot) whereas the adults have  3 segments.