One of the hallmarks of bed bugs are the little black dots of excrement that bed bugs leave behind on furniture. In fact, when searching for bed bugs, the little black dots will likely be the first evidence found. Sometimes the infestation is so small that finding the actual bug in a crack or crevice is very difficult and one must put greater credence on the black dots. But often furniture naturally has black dots. How does one decide what is bed bug evidence and what is natural?
The first line of deduction is to examine the patterns of the black dots. Often bed bugs will cluster around an imperfection in a piece of wood with the black dots immediately around the imperfection. If you find a black dot in the middle of a flat surface it is less likely to be bed bug related.
A second method of deduction is to note where the black dots are in relation to the furniture. Bugs like to be hidden against the wall so dots out in the open are less likely bug related. Also bugs have very specific likes and dislikes for harbourage with raw wood and cloth being favourites. For example black dots on the wooden slats under the mattress of a captain’s bed are likely bed bug related.
A third method of deduction is to wet your finger and smear the black dot for a few seconds. If the dot is part of the furniture it will not smear. If the dot is bed bug excrement it will smear as it is actually dried blood. This method works best on hard surfaces as the blood could not absorb into that substrate. Black dots on rough wood are a little tricker because the blood will partially absorb into the substrate making smearing less obvious. The smear test works poorly on cloth because the fabric readily absorbs the blood making smearing difficult. On the other hand cloth is less likely to have random black dots so cloth with black dots is again likely bed bug related.
Determining bed bugs via the black dot method is sometimes tricky. With experience one can take the above three methods and combine them into a reasonably accurate assessment.