The Blue Dacnis is a stunning inhabitant of humid lowland forest from Honduras to south to northeastern Argentina. The Blue Dacnis is sexually dimorphic: the male primarily is bright turquoise blue with a black throat, back and tail, whereas the female is mostly green with a blue crown. Blue Dacnis are most often found foraging for nectar and insects in the tops of trees along forest edges or small clearings. When foraging for insects, the Blue Dacnis usually takes its prey from leaves, often with acrobatic maneuvers; the Blue Dacnis frequently pays particular attention to brown spots on green leaves, apparently seeking out leaf damage that might indicate the presence of an insect.
The common name for this species in Spanish is the Dacnis Azul (Hilty 2011, de Juana et al. 2012), and in Portuguese it is Saí-Azul (CRBO 2010). The etymology of Dacnis comes from the Greek daknis, an unidentified bird from Egypt (Jobling 2010). The specific epithet cayana was used along with cayanensis and cayanus in to refer to Cayenne or French Guiana; Cayenne was often used for species that were from an uncertain province thought to be in the Amazon (Jobling 2010).