Creature Feature: Common Buckeye

Junonia coenia_9_26_18_Ezra Staengl.JPG

Common Buckeye (Junonia coenia)

Common Buckeye

Junonia coenia

Family: Nymphalidae

Distinguishing Features/Description

Common buckeyes are medium sized, brightly colored and strikingly patterned butterflies.  Each of the buckeye’s four wings have two dark colored eye spots circled in a thin band of yellow.  The eye spots are positioned along the edges of the wings, and the two central ones on each side of the body are the largest.  The large eye spots on the forewings are surrounded by a thick white band, the shape and color of which are important identification features for separating this species from the other two North American buckeyes.  The leading edges of the forewings between the body and these white patches are brown, interrupted by two orange to red vertical lines parallel to the body.  The hindwings are mostly brown around the eye spots, with orange and yellow bands on the trailing edges.  The underside of the forewings is similar to the upperside, while the underside of the hindwings is much duller, with smaller less colorful eye spots and less patterning.  In the fall you might see common buckeyes “Rosa” form, with much brighter, pinkish hindwings.

The common buckeye is named after the resemblance of its eye spots to the eyes of male deer (bucks).  Interestingly, Native Americans named the buckeye trees with an indigenous word meaning buck eye, due to the nuts’ resemblance to bucks’ eyes, but there is no other apparent connection between the tree and the butterfly.

Common buckeye is the only buckeye in Virginia, so it is difficult to confuse with other butterflies in the state.  Two other buckeye species do live in the United States however, the mangrove buckeye in Florida and the tropical buckeye in Florida, Texas and the Southwest.  Both other buckeye species are duller, with smaller eye spots and not as bright colors compared to common.  Mangrove buckeye has orange instead of white bands on the forewings, which are bordered on the inside by black.  Tropical buckeye has very thin pinkish bands on the forewings and is much darker than common in general. 

Junonia coenia_9_26_18_Ezra Staengl-2.JPG

Common Buckeye (Junonia coenia)

Distribution and Habitat

Common buckeyes can be found throughout the southern United States year-round, but their range extends up to southern Canada in the summer months.  They are absent from much of the west, including Montana, Idaho and the surrounding states.  They are also present in Mexico and some of the Caribbean.

In Virginia common buckeyes can be found in a variety of open sunny habitats throughout the state.  They are present in many disturbed habitats, such as roadsides and pastures, as well as the many types of natural grasslands in the state, such as woodlands, savannas and prairies.  Common buckeyes can be found anywhere their generally prairie affiliated host plants can be found.

Ecology

Caterpillars are generalists on a wide variety of herbaceous plants, including plantain and wild-petunia.  Adults feed on nectar from a variety of plants, but the Asteraceae seems to be a favorite family.

On September 26th, 2018 CUH surveyed a piedmont prairie growing in a powerline right of way in Albemarle County.  We observed common buckeye caterpillars feeding on Agalinis purpurea (purple false foxglove), and adults in great numbers on Euthamia graminifolia (common flat-topped goldenrod).  The flat-topped goldenrod was growing in a large patch in the middle of a large and exceptionally biodiverse piedmont prairie remnant in a high-tension powerline right of way.  It was in the peak of its bloom, and the flat clouds of yellow flowers stood out from the surrounding broomsedge and other prairie grasses. Butterflies, moths and other insects including fiery skippers and swarms of common buckeyes fed from the flowers. Almost every flat-topped goldenrod flower had several buckeyes on it, the eye spots on their wings reflecting the sunlight in a dazzling array of iridescent colors.

Junonia coenia on Euthamia_9_26_18_Ezra Staengl.JPG

Common Buckeye (Junonia coenia) on Common Flat-topped Goldenrod (Euthamia graminifolia)

The scene above illustrates a couple of ecological relationships between the Piedmont prairie plant community and the common buckeye.  Many possible host plants for the buckeye grow in the prairie, including wild petunia and purple false foxglove, the latter of which we directly observed the buckeye caterpillar eating.  The prairie is also full of good nectar plants for migrating and resident adult butterflies, with the flat-topped goldenrod stealing the show in this scene.  The buckeyes, like other insects that feed on nectar, are inadvertently pollinating the plants they are feeding on.

Although we did not observe any predation of adults or caterpillars, they undoubtable serve as food sources for birds and predatory insects living in the powerline right-of-way.  The caterpillars are covered with thick dark spines, possibly serving as a physical defense from such predation, and of course the adult butterflies have the brightly colored eye-spots, which may serve as a distraction to predators.

Like the famous monarch, common buckeyes are at least partially migratory, with the first brood in the south of their range moving up into the northern US and southern Canada in the spring.  Different individuals fly back south in the fall, causing a peak in the numbers of common buckeyes in Virginia during their migration period.  Common buckeyes fly in Virginia roughly from May to October, with pupae surviving the winter.  They fly all year in the deep south but only briefly and sporadically in the northern part of their range during summer.

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