Butterfly Mimicry

From the researcher's perspective...

Ghosting along the forest floor of the deep shady ACG, Pierella helvetia is one of the few large ACG butterflies that can be reliably encountered on a non-rainy day by walking a rain forest trail slowly and observantly for hours. Perched motionlessly, wings closed on the fallen and dark rotting leaves, this butterfly is close to invisible. The bright red of the upperside of the hind wings is not displayed until the butterfly launches into fast darting flight among the leafless plant bases sticking up out of the litter, and then perches again, the red “tracking patch” having abruptly disappeared. Additionally, the large false eye spot on the upper corner of the hind wing upperside is matched by a yet more well-defined false eye spot on the underside. Somewhat cryptic at a distance, but quite convincing close up, this pattern is evolutionarily designed to give the butterfly a few seconds head start in its flight from a startled potential predator.
Today P. helvetia is placed in the large family Nymphalidae, but for the past century or more it would have been placed in the Satyriidae, today a Satyriinae subfamily of Nymphalidae. In the lowland tropics, satyrines, as their name implies, are basically brown and soft-winged forest shady understory species with quick and often interrupted flight and very often having false eyes on the wings. Though many extra-tropical species have the same flight pattern, there are also many satyrines of meadows, field edges and other more insolated circumstances. Throughout, whether large or small, the caterpillars feed on monocots—grasses, sedges, palms—and even some yet more primitive plants. None eat the leaves of broad-leafed plants, the angiosperms. P. helvetia is no exception, with its finely brown-and-gray-mottled caterpillar feeding on the leaves of understory Calathea (Marantaceae) and Heliconia (Heliconiaceae). There is even one rearing record from a sedge (Cyperaceae). The caterpillar usually feeds at night, hiding motionless during the day low down on the stem or even in the litter at the base of the food plant. In ACG, P. helvetia is the rainforest Pierella while the similar but red-patch-lacking Pierella luna occupies the interface between dry forest and rain forest, its caterpillar feeding on the same food plants and behaving the same way.