Walking in the forest at night, a glint caught my eye from the side. The shimmer seemed different from eyeshine, almost crystalline in its reflection. As I approached, rows of black dots began to take form and its white shimmer grew into deep gold. Suspended here was the chrysalis of a tiger ithomiine butterfly (Tithorea tarricina). It stayed completely motionless as I overturned the leaf to inspect it, and water droplets clung to its sides like tiny marbles. I think few structures in nature come close to the beauty and elegance of a butterfly chrysalis, even more so one that is metallic yet not uniform, with black accents revealing its symmetry. Antennae, eyes, mouthparts, wings, legs— all the external anatomy of an adult butterfly can be picked out on this idle transformer.
This species belongs to a tribe of butterflies that predominantly has translucent wings (called clearwing or glasswing butterflies), which are almost invisible as they fly through the forest understory. Tithorea tarricina, however, displays a rusty red-orange color on the hindwings and light-colored spots ornament its dark wings. It is a co-mimic of Heliconius hecale, both members a group of unrelated butterflies which have evolved to look very similar to one another— in what has been called the ‘tiger’ mimicry ring. Because both T. tarricina and H. hecale are distasteful to predators, both species benefit from the increased advertisement of their color pattern to predators. The argument goes that if a bird predator has a bad experience attempting to consume one of the two species, that same predator will be less likely to try to eat the other species that looks nearly identical. At the population level, predation is reduced due to the higher numbers of these distasteful mimics fluttering around. Co-mimics are also known to have similar behaviors and habits in nature, and one of the most fascinating observations is that they may roost together gregariously at dusk. During the day, the butterflies will disperse to forage and find mates, but individuals will remember the location of their roost site and return every night. This behavior, too, is likely driven by bird predation. It reduces the chance an individual is successfully captured (like in schools of fish!) and perhaps also provides a more conspicuous and memorable signal to predators. If I was a predator that attacked a roost one night and had a nauseous experience, I certainly would be less likely to do so again the next!
