Although sometimes considered a subspecies of the Blue-tailed Emerald (Chlorostilbon mellisugus), the Red-billed Emerald is often regarded as its own species. Males differ in appearance from the Blue-tailed Emerald by having a mostly red lower bill, but females look almost identical to female Blue-tailed Emeralds in the field. Males and females can sometimes be told from other hummingbirds in this genus by their stone bluish black tails. Red-billed Emerald inhabit dry, shrubby regions including woodlands, partially open areas, parks, gardens, and desert scrub. They feed on nectar at low, scattered flowers and often select short tubular flowers that are more commonly visited by insects than other hummingbirds.