Bed bugs (Cimex lectularius) are small parasitic insects that feed exclusively on the blood of warm-blooded animals. These pests do not discriminate among available hosts; the idea that an infestation targets only one individual is an inaccurate myth. Bed bugs are driven purely by biological necessity and will feed on any accessible person or pet. The perceived selectivity reflects the differing ways human bodies react to the bites, not the insect’s preference.
How Bed Bugs Locate a Host
Bed bugs are not searching for a specific person’s blood type or gender, but rather for generalized, non-selective cues that signal a host is nearby and inactive. The primary attractant for these insects is the carbon dioxide (CO2) exhaled during breathing, which acts as a long-range signal of a sleeping host. They are highly sensitive to even small increases in CO2 concentration, allowing them to orient themselves toward the source in the dark.
Once closer, the second major cue that guides the bed bug is the host’s body heat, or thermal signature. The average human skin temperature is significantly warmer than the surrounding environment, and bed bugs use this temperature gradient to locate the precise feeding spot. They also detect chemical signals, such as volatile compounds or pheromones emitted from the skin, which help them confirm the host’s presence.
These insects have evolved senses that prioritize the universal signs of life, meaning any warm, breathing body in the vicinity is a potential meal. Their feeding drive is a response to these simple, powerful biological triggers, ensuring every person in an infested room is equally at risk of being bitten.
Why Bite Reactions Are Not Universal
The reason an infestation may appear to only affect one person lies entirely within the variability of the human immune system, not in the insect’s choice of host. When a bed bug feeds, it injects saliva containing an anesthetic to prevent the host from feeling the bite, along with an anticoagulant to keep the blood flowing. The resulting visible bite mark, or welt, is an allergic reaction to the foreign proteins in this injected saliva.
Individuals vary greatly in their sensitivity to these proteins. Some people develop a large, immediate, and intensely itchy reaction, while others may experience a delayed reaction that takes several days to appear. A large portion of the population, estimated to be between 30% and 70%, may exhibit no visible reaction to the bites at all, even after being fed upon repeatedly.
The concept of sensitization also influences the visibility of bites. A person new to an infestation may not react to the first few bites. With repeated exposure, the immune system may become sensitized, causing reactions to appear or intensify over time. The latency period between the bite and the visible welt often decreases. Therefore, the person without visible marks is still being bitten; their body simply does not mount a noticeable allergic response, which is why focusing on bites alone is an unreliable way to confirm an infestation.
Confirming an Infestation Without Visible Bites
Since relying on a lack of bite marks is not a reliable indicator that a room is clear, confirmation of an infestation requires searching for physical evidence left behind by the insects themselves. Inspection should focus on areas where bed bugs hide during the day, which are typically within a few feet of the host.
Physical Evidence
One of the most common and telling signs is fecal spotting, which appears as small, dark, ink-like stains on bedding, mattresses, or walls. These spots are digested blood and will smear slightly if wiped with a damp cloth, which distinguishes them from common dirt or mold.
Another clear sign of bed bug activity is the presence of shed skins, also known as exuviae. As the young insects, or nymphs, grow, they must molt, leaving behind translucent, empty casings that resemble the shape of a bed bug. These shed skins, along with tiny, pale yellow eggs and eggshells, are often found clustered in the insect’s preferred hiding spots.
Inspection Areas
Look closely along the seams, piping, and tags of the mattress and box spring. Other common harborages include:
- Cracks and crevices in the bed frame.
- Behind the headboard.
- The joints of bedside furniture.
Finding any of this physical evidence confirms an infestation, regardless of whether any occupant shows bite reactions.