Shine on

Erin P. from Guam snapped these fascinating photos of a chrysalis in her garage and wanted to know what could possibly emerge from something so incredible as this silver and gold metallic-looking pod.

This shimmery confection of a chrysalis will soon give way to a Common Crow (Eupola core) butterfly. Common to South Asia, India, Austrailia and Guam these glossy black butterflies with white spots are a common site and appear quite dull in comparison to their remarkable chrysalis.

The Common Crow is a member of the Danaid group of the Nymphalidae (or brush-foot) Family. Danaids are well protected from predators as most species in this group are somewhat toxic. As caterpillars, Common Crows consume Oleander (Nerium oleander) and some other closely related plants. Oleander contains toxic compounds in its milky sap that the caterpillars are able to process and sequester in their bodies making them incredibly distasteful to predators.
The gorgeous gold and silver coloration of the chrysalis is not actually anything metallic but instead is a trick of light caused by layers of mostly transparent pupal skin refracting light.

Refraction occurs when light "bends". Sometimes light rays pass through differing transparent mediums, such as from air to water. These different mediums can cause the light rays to arrive at your eye at different times and from different directions.

Refraction changes the direction of the light rays creating a variety of lighting effects. Light rays bending through the layers of transparent chrysalis skin create this metallic or iridescent effect, similar to the iridescent blue tones of a Morpho butterfly's wings.

This same bending of light rays can also be observed if you put a stick half into water. At the point where the stick enters the water it will appear to bend. For more on light refraction try this site.

Here in Florida the chrysalids of the Zebra longwings, Julia, Gulf Fritillary, Queen and Monarch butterflies all have small areas that appear metallic from this same type of light refraction.