Common Buckeyes (Junonia coenia) are among our most widespread and easily recognized butterflies.
Common throughout much of the U.S. and southern Canada, they’re found in open, sunny areas — fields, roadsides, weedlots, gardens, and sand dunes. Males spend much of their time patrolling in search of females and perching on low vegetation with widespread wings.
As butterflies go, Buckeyes are small to medium-sized, and their brownish wings bear distinctive orange and cream markings, plus several prominent eyespots. Studies suggest that the eyespots may frighten off birds and other predators, or they may divert strikes to the wings instead of the butterfly’s body.
I’ve seen still-active Buckeyes with conspicuously tattered wings, suggesting numerous encounters with predators. Other observers have reported Buckeyes flying normally even when two-thirds of their wing surface was missing.
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Buckeye larvae are black and spiny with white and orange markings. Eyespots won’t develop till later, while they’re in the chrysalis stage, metamorphosing into winged adults. Instead, there’s a different anti-predator defense operating at this stage in the life-cycle.
The caterpillars feed on a variety of plants, including fogfruit, plantain, toadflax, twinflower, false foxglove, and some others. One thing all these plants have in common is that they contain chemicals called iridoid glycosides, bitter substances that literally stimulate the caterpillars’ appetites, promoting vigorous feeding behavior and presumably faster growth. But these glycosides apparently diminish growth in animals that tend to eat Buckeye caterpillars, and studies suggest that ants, wasps, birds and other potential predators avoid larvae with high concentrations of iridoid glycosides stored in their bodies.
There’s more to the story.
Buckeye butterflies that are ready to lay their eggs actively seek out plants rich in these predator-deterring substances. After alighting on a possible larval food source, the female starts tapping the leaf surfaces with her spiny legs. This “drumming” behavior releases plant juices that the butterfly then “tastes” and evaluates via a rich array of chemoreceptors on her legs and feet.
In the warmest parts of their range, Common Buckeyes produce multiple broods throughout most of the year. Although they’re listed as resident in the Carolinas and may overwinter as adults, they can’t tolerate extended freezes.
In the northern parts of their range, large numbers of Buckeyes start moving southward in the fall to Florida, the Gulf Coast, and other warmer locations. Successive generations of these migrants will gradually re-populate the country during the following spring and summer.