A butterfly’s wing is covered in thousands of tiny scales, most of them there for color. But on many adult males, a few patches of scales do something else entirely: they make a sort of species-specific perfume. These are scent scales, and the patches they form are called androconia.
Androconia patches
The name comes from the Greek for “male dust,” a fitting label for the powdery scales a male uses to court. Androconia patches are clusters of specialized scent scales on the wings of adult male butterflies and moths. They produce and release pheromones that attract females, advertising the male’s species identity, his readiness to mate and his vitality.
They are often visible to the naked eye. Look for:
- dark patches or velvety spots on the forewings or hindwings
- streaks or lines along the wing veins, often called “sex-brands” or “stigmata”
- in milkweed butterflies such as monarchs and queens, brush-like hairpencils that the male everts to waft scent toward a female
Scent scales up close
Under a microscope, scent scales look nothing like ordinary wing scales. They come in distinctive shapes, among them rod-shaped, lamellar (plate-like) and paddle-shaped forms. Their surfaces carry ridges and tiny apertures or pores that help the scent escape and disperse into the air, turning each scale into a miniature diffuser.
The chemistry of a butterfly’s perfume
Butterfly scent is chemically richer than its reputation suggests. A 2023 review by Stephanie Ehlers and Stefan Schulz, covering research from 1990 to 2022, found that butterflies draw on a wide palette of volatile compounds, including alkaloids, terpenoids, fatty acid derivatives and aromatic compounds, some with structures unique to butterflies (Ehlers & Schulz, Nat. Prod. Rep.).
Two patterns stand out:
- The roles are reversed. In night-flying moths, females are usually the scent producers. In butterflies, scent emission is mostly a male affair, which is why androconia are male features.
- The range is short. Bright wing colors draw a female from a distance; scent usually works up close, during courtship itself. It is the final, intimate signal that confirms the right species and a worthy mate.
Compared with the more chemically uniform pheromones of moths, butterflies’ scent vocabulary is far more varied, and for many compounds scientists still do not know exactly what message they carry.
Leave a Reply