Adult bee hummingbirds typically weigh between 1.6 and 2.6 grams, with males at the lighter end. Total length is around five to six centimetres, much of which is bill and tail rather than body. No smaller adult bird is known from any living species.
Being this small carries a steep metabolic cost. Surface area rises relative to volume as an animal shrinks, so heat is lost quickly and the bird must feed through much of the day. Like other hummingbirds it enters torpor overnight, dropping body temperature and metabolic rate to survive the hours when it cannot feed.
Wing-beat figures for the species are often quoted with more precision than the measurements support, and reported rates vary widely with flight mode. The species is listed as Near Threatened, with habitat loss on Cuba the main pressure; how far its dependence on particular native plants limits its recovery is not fully settled.