The wire-crested thorntail is one of the smallest birds on Earth, with a mature weight of about . Males are about long, including tail extension, and females about . Adults of both sexes have coppery green upperparts with a white band across the rump. Males have a glittering green crown with a thin hair-like crest. Its
gorget is iridescent green, the flanks brownish with a white patch, and the rest of the underparts black. The tail is steely blue with white feather shafts, deeply forked, and the outer feathers are very narrow which with the crest give the species its common name. The female does not have the crest. It has a broad white streak on the cheek. Its underparts are black with a white patch on the flank. Its tail is short, only slightly forked, and bluish black with white tips. Juveniles are similar to the adult female. ==Distribution and habitat==