Glimmering sparkly gold in the sunlight, a question often asked is why is the Monarch chrysalis adorned with metallic dots and dashes? The gold dots serve the function of oxygen exchange but that doesn’t answer how and why the dots are gold.
Since time immemorial people have noticed the brilliant golden dots, dashes, and gold leafing of many species of butterfly chrysalides. The word chrysalis originates from the Greek word “chrysos,” which means gold.
There are are several hypotheses. The two that make the most sense are deterrents to predators and camouflage.
For the same reason the iridescent scales of the Blue Morpho Butterfly flash light when the butterfly is in flight, the golden markings of the chrysalis catch light, confusing and deterring predators.
Butterfly pupae are protein-rich easy targets. They are too busy rearranging their insides while undergoing metamorphosis to fend off predators. For the most part, throughout a butterfly’s life cycle, from caterpillar to chrysalis to adult, each species has evolved with specific-to-that-species warning and/or camouflage markings.
The chrysalis of the Black Swallowtail Butterfly is a perfect example. When the butterfly pupates in the spring and summer, the chrysalis has a soft golden green hue, which blends beautifully with the lush green of summer foliage.
When the butterfly pupates late in the summer, the chrysalis turns woody brown, taking on the same hues of bare tree branches.
Golden studs, dashes, and leafing reflect the surrounding area, create flashes of light, look like drops of dew, shafts of light, and is some cases, such as that of the Tigerwing Butterfly, may frighten a predator when it sees its own reflection.
Tigerwing Butterfly (Tithorea harmonia) Photo by Desus Mortus
How the gold is formed is easier to pinpoint. Metallic and iridescent markings in butterflies are created when both pigmented cells (in this case yellow carotenoids) and structural cells are present. You see carotenoids present when trees turn yellow, gold, and orange in autumn. The Monarch caterpillar gets its carotenoids from the plant it eats, milkweed.
The crown of the Monarch pupa is called a diadem. If you look closely at the diadem, it’s a raised structure, a line of tiny hills. The combination of the raised hills and carotenoids present both absorb and reflects the light, creating the appearance of shiny gold.
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