Swallowtail butterfly chrysalises vary in color, even within the same species.
The color of a butterfly chrysalis is determined by genetics. Along with genetics, the color of some species’ chrysalises are also determined by their surroundings when they pupate.
In areas of the US where winter comes early, it appears that Black Swallowtail chrysalises that are in diapause are always brown chrysalises. Many people assume, logically, that brown means that the chrysalis is in diapause. In areas where winter is shorter and more green plants are growing when the last generations pupates, it becomes evident that color of a chrysalis, whether in diapause or not, depends upon the surroundings of the pupating caterpillars.
There are theories about the quality of the host plant and diapause. We have conducted several tests to determine what causes a chrysalis to pupate brown and to pupate green. We have not conducted tests with varying qualities of host plants. In our tests, all caterpillars were fed the same food, from the same plants.
In one experiment, we placed large Black Swallowtail caterpillars in cups that were lined with different colored paper. A small amount of host plant was placed in the bottom of each cup. The tray of cups was placed 2′ below a bright fluorescent light. After all caterpillars had pupated, colors of the chrysalises were compared to the colors of the paper.
In the other experiment, caterpillars were placed in small mesh containers, lined with different colored paper, in a bright window. After all had pupated, the chrysalis colors were compared to the paper colors.
It was clearly demonstrated that the color of a Black Swallowtail chrysalis depends upon the color of its surroundings.
So why are chrysalises in diapause normally brown? Simple. In the fall, when they go into diapause, most of their surroundings are brown. Green leaves have begun to turn fall colors. Few plants are growing fresh green leaves.
Most swallowtail butterflies will be either green or brown (or somewhere in between). In some cases, they may take on an unexpected color. The top photo of this page is of four Black Swallowtail chrysalises. One is a teal blue. It had pupated on a teal blue plastic container in bright light. Another is a white/yellow color. It pupated on a white plastic container in bright light. Normally this species pupates only brown or green.
Some species, like Buckeye and Mourning Cloak, pupate into the same color with only a variation of shade. They can range from super dark (nearly black) to super light.
Cloudless Sulphur chrysalises can pupate into a wide range of color. The one that is deep purple pupated on a black mesh screen.
Palamedes Swallowtail green chrysalises are the color of living leaves of one of their host plants, Red Bay. Brown/rust chrysalises are the color of dead leaves of the same tree.
Phaon Crescent chrysalises will vary in shades of brown according to where they pupate.
Although many species chrysalis color depends greatly upon where they pupate, Queen chrysalis color is determined by genes, not the location of where they pupate.
Jodi Hopper, of Wish Upon a Butterfly in Pennsylvania, found a few yellow chrysalises among her green Monarch chrysalises. She determined that the color was caused by a recessive gene. When Monarch butterflies emerged from the yellow chrysalises, they were normal colored adults. But when they paired and laid eggs, their offspring would pupate only as yellow chrysalises.
When feeding caterpillars in our lab one day, we decided to take a photo of Zebra Longwing chrysalises on two lids. The chrysalises on a white lid were very light in color. Chrysalises on the darker blue lid were dark in color.