Junonia coenia, known as the common buckeye or buckeye, is a butterfly in the family Nymphalidae. It is found as a resident or vagrant across much of North America and Central America, as well as in parts of northern South America. This includes most of the eastern half of the US, the lower to middle Midwest, the Southwest (including most of California), southern Canada, and Mexico. Its habitat includes fields, dunes and scrub, typically in sunny environments up to 1,300 metres (4,300 ft) in altitude. It can be found in open areas with low vegetation and some bare ground. Its original ancestry has been traced to Africa, which then experienced divergence in Asia. The species Junonia grisea, the gray buckeye, is found west of the Rocky Mountains and was formerly a subspecies of Junonia coenia. Caterpillars of these butterflies appear to prefer plants that produce iridoid glycosides, which are bitter compounds that release a hormone called gastrin that activates the digestive system (i.e. hunger); therefore, iridoid glycoside producing plants stimulate and attract their appetites particularly when found in plants like Plantago lanceolata. In fact, the presence of these metabolites may trigger oviposition behaviors in female butterflies so that descendant larval bodies may better incorporate iridoid glycosides. Iridoid glycolyside metabolites appear to have a growth-stimulating effect on caterpillars but a growth-reducing effect on predators. Predators like ants, wasps, birds, and small animals prefer to feed on iridoid glycoside poor caterpillars rather than iridoid glycoside rich larvae, potentially due to these effects. Therefore, immunity of J. coenia larvae to predators like ants appears to be strongly related to the concentration of iridoid glycosides sequestered in their bodies. However, too much iridoid glycosides in the diet can negatively affect the immune response of these larvae and lead to increased susceptibility to parasitism.
Adult butterflies feed on flowers with certain pollinator cues: yellow flowers that are "pre-change", or flowers whose color has not been changed due to insect visitation or other factors. Common buckeye caterpillars feed in isolation rather than relying upon grouping behaviors. Vulnerability to the Junonia coenia densovirus is another concern for survivorship of common buckeye larvae.
Description
Adult butterfly
Common buckeye butterflies are colored mostly brown with some orange, black, white, blue, and magenta. The forewing features two proximal orange bars and a postmedian white band, which surrounds a prominent black eyespot and borders a smaller, more distal eyespot; both eyespots have a bluish center and each border a distal orange mark. The hindwing is mostly brown with an orange band towards the edge and a brown and white margin. It also has two eyespots, one larger and one smaller, each with a black and white outline 2 and 2.5 inches (5–6.5 cm).
Caterpillar These caterpillars have a beautiful and complex color pattern. Their backs are mostly black with light-colored markings (white, gray, beige, or brownish, varying among individuals—see picture below), their sides have white markings and red-orange spots, and they have a brown underside. They have a mostly red-orange head with black markings on the face. They have spines running lengthwise along their back and sides, as many as 7 per segment. There is also a pair of small spines on the top of their head. These spines branch out (have smaller spines coming out of them) and appear a bit shiny-blue at the base. They also have 2 pairs of tiny white spines on each segment, near the bottom. The color patterns and spine forms are less pronounced in earlier instars. There are several other species that resemble these caterpillars in appearance, such as the painted lady, the Glanville fritillary, and the red admiral, which can be easily confused by an untrained observer. They can reach 4 cm (1 5/8 inches) in length.
Pupa (chrysalis) Like the more familiar monarchs, these caterpillars pupate by spinning a silk pad on a downward facing horizontal surface, attaching themselves with their rear end, and hanging in the form of the letter J for a day or so before shedding their skin to reveal the chrysalis. The chrysalis is mostly brown with beige markings, and has a prickly texture. It has a beige band near the top, another one at the "waist" (border between thorax and abdomen), and 4 pairs of beige dots running down its dorsal side. It is 18 mm long and 8 mm wide. When touched or handled excessively, it has a habit of wiggling its abdomen.
Phylogeny Junio probably arose from one African colonizing ancestor. In Asia, this diverged into J. atlites, J. iphita, and J. hedonia that resembled the African ancestor. These species then diverged into J. almanac, J. lemonias, and J. villida that began to differ morphologically from African ancestors. The Taxon Pulse Hypothesis is invoked to explain the vicariance as well as dispersal exhibited by this species where there is dispersal as the species expands until they find appropriate habitats. This then allows for speciation to occur in several isolated habitats. In Junonia the species may have expanded from Africa into Asia and then from Asia throughout "Australasia, Africa, and South America." In the 1930s established populations were recognized in Cuba and the Florida Keys. In the 1940s populations migrated inland from the coast of Florida and further into the southern United States.
Food resources
Caterpillars Caterpillars feed on a variety of plants including the narrowleaf plantain (Plantago lanceolata), the common greater plantain (Plantago major), blue toadflax, false foxglove, Mexican petunia (Ruellia species), the firecracker plant, and cudweed.
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