Bed bugs are elusive and usually nocturnal (peak activity usually occurs between 10:00 p.m. – 6:00 a.m.), which can make their detection difficult. They often lodge in dark crevices, and the tiny adhesive eggs can be nestled by the hundreds in fabric seams. Aside from bite symptoms, signs include fecal spots (small dark sand-like droppings that occur in patches around and especially beneath nests), blood smears on sheets (fecal spots that are re-wetted will smear like fresh blood), and the presence of their empty molted exoskeletons.

Although bed bugs can be found singly, they tend to congregate once established. Although they are strictly parasitic, they spend only a tiny fraction of their life cycles physically attached to their hosts. Once feeding is complete, a bed bug will relocate to a place close to a known host, commonly in or near beds or couches in clusters of adults, juveniles, and eggs which entomologists call harborage areasor simply harborages to which the insect will return after future feedings by following chemical trails. These places can vary greatly in format, including luggage, inside of vehicles, within furniture, amongst bedside clutter, even inside electrical sockets and nearby laptop computers. Bed bugs may also nest near animals that have nested within a dwelling.