Bed bugs (Cimex lectularius) are small, parasitic insects that feed exclusively on the blood of humans and animals. Although classically known for nocturnal activity, the answer to whether they bite while a person is awake is yes. Bed bugs are opportunistic; they adjust their feeding schedule based on the host’s habits or hunger, which can lead to biting during daylight hours or when a person is sedentary but awake.
Nocturnal Feeding Habits
The common bed bug prefers feeding at night, typically between midnight and 5:00 a.m. This timing is an adaptation to take advantage of human hosts when they are most still. The insects are drawn primarily by the carbon dioxide (CO2) exhaled during respiration, which acts as a long-range chemical cue.
As they approach, bed bugs use body heat as a directional signal to pinpoint the feeding location. Once the skin is pierced, the bug injects saliva containing an anesthetic and an anticoagulant. This prevents the host from feeling the bite and ensures a steady blood flow. A single feeding session lasts three to ten minutes, after which the bug retreats to a nearby hiding spot, or harborage, to digest its meal.
Exceptions to the Nighttime Rule
Although bed bugs are predominantly nocturnal, their need for blood supersedes adherence to a nighttime schedule. They will bite during the day or when a person is awake if they are sufficiently hungry. Bed bugs typically feed every three to seven days but can survive for weeks or months without a blood meal.
An opportunity for a daytime meal arises when a host is present and stationary for an extended period, such as someone sleeping during the day or lounging on an infested sofa. Heavy infestations can lead to competition, forcing some bugs to seek a meal at abnormal times. If a harborage is accidentally disturbed, the agitated bed bugs may scatter and seek an immediate blood meal regardless of the time.
Physical Characteristics of a Bite
The bite itself is generally painless due to the anesthetic properties in the bed bug’s saliva, meaning most people do not feel it happening. A reaction to the bite may not appear for up to two weeks, which makes identifying the source difficult. When a reaction occurs, the bites typically appear as small, red, itchy bumps, sometimes evolving into larger welts or blisters.
A common pattern is a linear or zigzag grouping of three to five lesions on exposed skin, sometimes called the “breakfast, lunch, and dinner” pattern. Bites are usually found on areas exposed while sleeping, such as the face, neck, arms, and legs. Individual reactions vary widely; some people show no visible marks, while others may experience a severe allergic response.
Evidence of an Infestation
Since bite marks are an unreliable indicator, confirming the presence of bed bugs requires looking for physical signs.
Fecal Droppings
One key piece of evidence is the presence of dark, tiny spots on mattresses, box springs, or bedding. These dried fecal droppings are digested blood that appears black or dark brown.
Shed Skins and Live Bugs
Another sign is the discovery of pale yellow, translucent exoskeletons (molts) that nymphs shed as they grow. Live bed bugs are flat, reddish-brown, and about the size of an apple seed. They can be found by inspecting mattress seams, cracks in the bed frame, and behind the headboard.