The common bed bug, Cimex lectularius, is a small, blood-feeding insect. When an infestation occurs, one person may wake up consistently covered in itchy welts while their partner shows no signs of being bitten, leading to the perception of selective targeting. Bed bugs are not inherently choosy about their human host; the difference stems from the bugs’ generalized host-seeking mechanisms and a wide variation in human physiological responses to the bites. Understanding these behaviors and reactions offers a clear explanation for the mystery of “selective” biting.
How Bed Bugs Find a Host
Bed bugs locate hosts using universal biological signals emitted by all sleeping humans; they are not selecting a specific person. The primary attractant for a hungry bed bug is the carbon dioxide (\(\text{CO}_2\)) exhaled during sleep. Specialized sensory organs on their antennae detect the \(\text{CO}_2\) trail, guiding them toward the resting host, even in total darkness.
The secondary signal drawing the insects closer is the host’s body heat, or thermal signature, which they detect over short distances. These two cues, \(\text{CO}_2\) and warmth, are the universal indicators of a blood meal. The bugs do not discriminate based on factors like blood type, gender, or diet. The idea that bed bugs prefer one person’s blood over another is a misconception; they respond only to the most available source of these common biological signals.
The Truth About Bite Reactions
The core reason for the perception of selective biting lies in the individual human immune response to the insect’s saliva. When a bed bug feeds, it injects saliva containing an anesthetic and an anti-coagulant to numb the bite and ensure steady blood flow. This injection makes the feeding process painless, allowing the insect to feed undisturbed for about five to ten minutes.
The visible, itchy welts that appear later are a delayed allergic reaction to the proteins in the bug’s saliva, not the initial puncture. A significant portion of the population, estimated to be between 20% and 70%, shows little to no visible skin reaction to the bites, even when consistently fed upon. These individuals are considered asymptomatic; they are bitten just as often, but their body does not mount a noticeable inflammatory response.
For those who do react, the severity and timing vary widely, ranging from small red spots to large, intensely itchy welts. The body often needs multiple exposures to the saliva before developing sensitivity. Once sensitized, subsequent bites can cause reactions that appear much faster, sometimes within hours, reinforcing the feeling that only the reactive person is targeted. This disparity between individuals who display a severe reaction and those who show nothing explains why one person may feel singled out.
Proximity and Infestation Clustering
Even if everyone in a home is equally susceptible to being bitten, the physical logistics of an infestation can lead to one person receiving a disproportionate number of bites. Bed bugs are considered “lazy” feeders, preferring to remain close to their host to minimize travel distance for a blood meal. Their preferred hiding spots, or harborages, are typically found within a few feet of the sleeping area, often in mattress seams, bed frames, or headboards.
If the primary harborage is clustered next to one side of a shared bed or in one person’s dedicated sleeping furniture, that individual will receive the bulk of the feeding activity. The bugs emerge from the closest crack or crevice, feed, and quickly return to their nearby hiding spot. A sound sleeper who moves less during the night provides an easier, longer-duration target, which influences the number of successful feedings. While bed bugs can travel up to 50 feet, they take the path of least resistance, meaning the person closest to the infestation’s center will be the most frequent victim.