Invertebrates
Great Purple Hairstreak
Atlides halesus · also called great purple hairstreaks
As sunlight catches its wings at just the right angle, a great purple hairstreak flashes a vivid iridescent blue-green, a colour that seems to vanish again the moment the butterfly shifts position, tied entirely to a caterpillar diet of mistletoe growing high in the trees above.
Overview
The great purple hairstreak, Atlides halesus, is a large, vividly coloured butterfly native to forest habitat containing mistletoe-bearing host trees across a broad range of the southern United States. Its striking angle-dependent iridescent wing colour, complete caterpillar dependence on mistletoe, and considerable size within the hairstreak group make it one of the most visually dramatic small butterflies found in the American South.
A colour that depends entirely on the light
The great purple hairstreak’s most striking feature is not a fixed colour at all but a shifting iridescent effect, fully visible only when the wings happen to catch the light from just the right direction.
Status
Least Concern — widespread and common across suitable forest habitat containing mistletoe throughout the southern United States.
Great Purple Hairstreak: common questions
Why does the great purple hairstreak's colour seem to appear and disappear?
This species produces its vivid, iridescent blue-green colouration through microscopic scale structures on the wing that reflect light in a specific way, meaning the colour only becomes fully visible when the wings catch light at the right angle, causing the butterfly to appear duller or more vividly colourful depending on the viewing angle and lighting conditions.
Why does the great purple hairstreak depend on mistletoe?
This species' caterpillar feeds exclusively on mistletoe growing as a parasite on host trees, meaning the butterfly's entire early life cycle is tied directly to wherever suitable mistletoe happens to be growing, making mistletoe availability a key factor in where the species can successfully reproduce.
What are the thin tails on the great purple hairstreak's wings for?
This species has thin, thread-like tails extending from the hindwings, a feature typical of hairstreak butterflies generally that is thought to function as a false antenna, potentially misdirecting a predator's attack toward the wing margin rather than the butterfly's more vulnerable head and body.
How big is the great purple hairstreak compared with other hairstreaks?
This species is one of the larger hairstreak butterflies found in North America, noticeably bigger than many smaller relatives within the same broader hairstreak group, making it one of the more substantial and visually striking members of that group.