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Skinny or Fat, Always a Nuisance

The average adult bed bug (scientific name Cimex lectularius) is about ¼ inch (6 mm) long, round, and reddish brown in color. Although they are usually flat enough to slip into a crack the thickness of a credit card, adult bed bugs grow quite a bit in size when they feed and become football-shaped. Juvenile bed bugs range from the size of a pinhead or small sesame seed to the adult size as they pass through five stages of growth (instars). Before feeding, hatchling bed bugs are yellowish tan and can be hard to see. Once they feed and digest their blood meal, bed bugs develop a black spot in the belly, making them easy to identify. If you need help with identification, county Cooperative Extension Offices often provide identification services.

bed bug balanced on fingertip
Adult bed bugs can easily slip into crack the width of a credit card. Photo: NYSIPM. Click photo to see enlarged version.
newly hatched bed bug next to a poppy and sesame seed
From left to right - poppy seed, first instar bed bug, sesame seed. Photo: NYSIPM. Click photo to see enlarged version.
bed bug adult engorged with blood
An engorged adult bed bug. Photo: NYSIPM. Click photo to see enlarged version.

The closest relatives to bed bugs are the bat bug, Cimex adjunctus, and the tropical bed bug, Cimex hemipterus. Tropical bed bugs are rare in New York, but bat bugs are common and will bite humans when desperate. As their name suggests, bat bugs live with and feed on bats. They also behave differently, and may be observed climbing on walls or in other strange locations. They do not survive long without their bat hosts and do not infest the bed, couches or any places you would typically find bed bugs.

top half of bat bug
The "hair" on the "shoulders" of bat bugs are longer than the eye is wide. Photo: D. Clement, HGIC.  Click photo to see enlarged version.

As a blood-feeding species, bed bugs puncture the skin in search of blood. They inject saliva to ease the process, which usually results in itchy welts from an allergic reaction to their saliva. People vary in their reaction to bites from no reaction to severe reaction, including blisters or hives. Although bite reactions are commonly mild—itchy red welts—skin reactions cannot be used to diagnose a bed bug issue. Itchy red welts would be a reason to suspect bed bugs and begin looking for them, but welts alone do not mean you have bed bugs.

Another sign of bed bugs, and the best way to begin a bed bug inspection, is black fecal spots on mattress and bed frame surfaces. Those small spots are digested and excreted blood from the bug’s gut. Use a wet tissue to wipe it and, if the color on the tissue is rusty, it suggests that you are looking at bed bug poop. Again, it is best to use this evidence as a first step in looking for bed bugs.

bed bug fecal stain on mattress
Bed bug poop on a mattress. Photo: NYSIPM. Click photo to see enlarged version.

Bed bug eggs are bean-shaped, translucent white and very tiny (1 mm), yet visible. Like fecal stains, they don't move and provide excellent evidence of bed bugs.

bed bug egg and fecal stain on wooden ruler
Bed bug fecal stain and egg. Photo: NYSIPM. Click photo to see enlarged version.