Common Buckeye
Junonia coenia (Hubner, 1822), fam. Nymphalidae, P-no. 77a0831
Host plants: Hosts include members of the figwort (Scrophulariaceae), plantain (Plantaginaceae), and acanthus (Acanthaceae) families.
Date found(s): August 22, 2026
Location(s) found: Meramec State Park, Franklin County, MO
Notes: The common buckeye’s preferred hosts contain quantities of the bitter and toxic compounds called iridoid glycosides. The caterpillars sequester these compounds and gain considerable protection from them against predators like birds and wasps. However, this protection can come with a considerable tradeoff. High concentrations of iridoid glycosides have been shown to reduce the caterpillar’s immune system, making it incredibly vulnerable to parasitic wasps, flies, and deadly pathogens. To avoid this, female buckeye adults carefully taste potential host plants, striving for just the right amount of iridoid glycosides, prior to choosing the specific plant to oviposit upon.
For the common buckeye, the benefits of this chemical sequestration do not continue to the pupal and adult life stages. Larvae actively metabolize the iridoid glycosides, and these compounds have been shown to drop considerably in late fifth-instar caterpillars and eventually become undetectable in adults. Adults then adopt a different strategy of using warning coloration and patterning of the large “buckeyes” to deter would-be predators.
