Nineteenth-century naming worked from museum skins in the hand, where the pale reddish tinge low on the belly is visible. In life the bird is normally seen clinging to a trunk with its underparts pressed against bark, so the field impression is of a barred back and a red cap. Males carry red from bill to nape, females only on the nape.
The confusion is compounded by the red-headed woodpecker, a different species with an entirely crimson hood, which had already claimed the more useful name. Reports of red-bellied woodpeckers being misidentified as red-headed are common in bird-feeder records.
The species has been expanding north over the past century, now breeding into the Great Lakes basin and southern Ontario where it was formerly rare. Warming winters and the spread of bird feeders are both plausible contributors, but the relative weight of each has not been separated convincingly.