The Green Thorntail (Discosura conversii) is a small hummingbird that is a resident breeder from Costa Rica to western Ecuador. It occurs at middle elevations from 700-1400 m but may descend lower early in the wet season. In Costa Rica and Panama it is confined to the Caribbean slopes.

This is a forest canopy species. The nest is undescribed, but a published image shows a female constructing a nest on a thin branch, so it is presumably similar to other cup nests built by species such as the Green-breasted Mango. All hummingbirds lay two white eggs incubated by the female alone.

Green Thorntail has mainly green upperparts, a white rump band and a blackish lower rump and tail. It weighs just 3 g. The 10 cm long male has the long wire-like tail that gives this species its name and green underparts. The 7.5 cm long female lacks the long tail and has blackish underparts with a green breast band. She has conspicuous white moustaches

The Green Thorntail is usually silent, but may give a quiet chip. These birds visit small flowers including those of epiphytes and shrubs, and also take tiny flies and wasps. Breeding males perch on open branches and may give a dive display.