Unexplained spots on bed sheets are often one of the first signs that cause concern about a possible infestation. It is a common misconception that these spots are solely fresh blood from a bite, but their appearance is a strong indicator of bed bug activity. These reddish or dark markings serve as physical evidence, offering a clue to the hidden presence of these nocturnal pests. Learning to correctly identify these stains and distinguish them from other household marks is the initial step in determining if professional intervention is necessary.
The True Nature of Bed Bug Spots
The dark spots most frequently found on bedding are not fresh blood, but rather the fecal matter of the bed bug, which is composed of digested blood. Bed bugs excrete this waste following a blood meal as they condense the liquid components of the blood they consume. This digested blood is deposited wherever the insect travels or aggregates, often resulting in tiny, dark specks that resemble ink stains on fabric surfaces.
These spots appear dark brown or black because the hemoglobin in the ingested blood has been digested and oxidized upon exposure to the air. The color can vary depending on the age of the spot; fresh droppings may have a slightly more reddish hue, while older spots are distinctly black. A separate type of stain is the true fresh blood spot, which occurs if a bug is accidentally crushed while feeding or shortly afterward by a person rolling over in their sleep. This crushing releases undigested blood, resulting in a smear or a brighter red spot, but the dark fecal spots are the more consistent and common sign of an infestation.
Practical Identification and Location
The fecal spots left by bed bugs are remarkably small, measuring about 1 millimeter, or roughly the size of a pinhead. These spots are often found in clusters, especially on absorbent surfaces like sheets, where they soak into the fabric instead of beading up. They may also appear in small trails, indicating the path the insect took from its feeding location back to its hiding spot.
The most telling sign of bed bug activity is the location of these stains, which are concentrated in areas where the pests hide or feed. Check along the seams, piping, and tags of the mattress and box spring, as these dark, protected crevices are preferred harborages. Fecal spots are also commonly found on the sheets near the head of the bed, on pillowcases, and on the wooden or metal frame behind the headboard. In heavy infestations, the spots may even be visible on nearby walls, baseboards, or behind electrical outlets, indicating a wider migration pattern.
A definitive way to test a suspicious spot is the “smear test,” which relies on the composition of the fecal matter. Gently apply a damp cloth, tissue, or cotton swab to the spot. Because the spot is made of dried, digested blood, a genuine bed bug fecal spot will smear or bleed out into a reddish-brown or rusty-colored streak when moisture is applied. If the spot remains dry, flaky, or does not dissolve into a reddish color, it is less likely to be bed bug excrement.
Ruling Out Other Household Stains
It is easy to mistake other household marks for bed bug fecal spots, but examining the stain’s texture and behavior can help differentiate them. Rust stains, for instance, may share a similar color but are dry and flaky, and they will not smear or dissolve into a reddish-brown color when tested with a damp cloth. Mold or mildew, which can appear as dark spots on mattresses, often have a fuzzy or greenish appearance and are structurally different from the concentrated, ink-like consistency of a bed bug dropping.
Another common confusion is with the residue left by crushed insects, such as mosquitoes or flies. While these do leave blood or dark smears, they often contain visible insect fragments or appear as singular, large, accidental smears rather than the small, clustered dots of bed bug feces. Stains from minor cuts or scratches on the skin can also leave blood spots on sheets, but these are generally localized and do not appear alongside other evidence like shed skins or in the crevice-based locations typical of a bed bug harborage.