The Long-tailed Sylph is member of a genus with long tails, with the Violet-tailed Sylph being the other species that can be readily found in Colombia. The Long-tailed is overall very green, with a glittering emerald patch on the front of the head. The wings are very long and extend far beyond the base of the tail. However its most definitive feature is its long tail, which can measure up to 12 centimeters in length and account for around two thirds of the overall length of the bird; this is a huge burden for the bird as it flies around from flower to flower in search of nectar. The female has a fairly short tail instead, a characteristic known as dymorphism, which is very common in bird species.