The Scarlet-thighed Dacnis (Dacnis venusta) is a tanager 4¾" long.
Iris bright red in male, duller red in female. Male unmistakable with bright turquoise blue crown and nape, sides of head and neck, centre of back, rump and scapulars.; forehead lores, sides of back, wings and tail, and mid-throat and entire remaining underparts black; the thighs are scarlet, but these are usually hidden. Female dull greenish blue above, brightest on cheeks, scapulars, and rump, duskier on back, wings, and tail; below dingy buffy greyish, buffiest on belly and undertail coverts.