Black-bellied Thorntail

The black-bellied thorntail weighs about 3.2 g (0.11 oz). Males are 12 to 13.7 cm (4.7 to 5.4 in) long and females 7.4 to 7.6 cm (2.9 to 3.0 in). Adults of both sexes of the nominate subspecies have an iridescent emerald green crown and coppery green upperparts with a white band across the rump. The male's gorget is iridescent emerald green with a golden coppery band below it. Its flanks are bronzy green and the rest of the underparts black. The tail inner feathers of the tail are steely blue and the outer three pairs gray; all have white shafts. The tail is deeply forked, and the outer feathers are very narrow which give the species its common name. The female's throat is white with green and black spangles and it has a thin white streak on the cheek. Its breast is spangled green with a coppery lower border; the belly is black with a white patch on the flank. Its tail is short, only slightly forked, and steely blue with bronze at the base and white tips. Juveniles are similar to the adult female. Subspecies D. l. melanosternon is slightly smaller than the nominate; its crown is grass green, the breast more golden, and the rest of the underparts darker.

The nominate subspecies of black-bellied thorntail is restricted to coastal eastern Brazil from southeastern Bahia south through Espírito Santo into eastern Rio de Janeiro. D. l. melanosternon is found in Amazonia of southern Venezuela, southeastern Colombia, eastern Ecuador and Peru, far northern Bolivia, and western Brazil. It inhabits the edges and interior of humid lowland forest generally at elevations between 100 and 300 m (330 and 980 ft). In Amazonia it is mostly found in terra firme forest but also occurs in the transition zone between terra firme and várzea.

The black-bellied thorntail feeds on the nectar of a wide variety of flowering trees and other plants. It mostly forages from the middle level of the forest to the canopy. It also feeds on arthropods, and a female has been observed apparently picking insects from a spider web.