How do leafwings escape predators?
By Chelsie Vandaveer
November 19, 2003
The goatweed leafwing (Anaea andria Scudder) is a member of the Nymphalidae, the brush-footed butterflies, and the subfamily, Charaxinae or leafwings. The butterflies are named for their characteristic trait--wings that appear like dried leaves. Leafwings are cryptic butterflies generally found in the tropics and subtropics. At rest, the goatweed leafwing keeps its wings folded together exposing the brown underside. It frequently hangs upside down even swaying slightly in a breeze.
Goatweed leafwings have both sexual and seasonal dimorphisms--males and females differ and wing shape and color varies slightly between summer and winter generations. The male's upper wing is orange edged with brown; the female's wings have a wide margin of brown and areas of lighter orange and dark brown.
The female lays one egg per leaf only on goatweeds, members of the genus Croton. When small, the caterpillar hides in plain sight by laying along the midvein of the leaf. After growing larger, the caterpillar constructs a tent by folding the edges of a leaf together and fastening it with silk. When fully grown, the caterpillar lays atop a rolled leaf.
Croton leaves are coated with stellate trichomes that make the leaves appear silvery. The leaves are rich in alkaloids and terpenoids. It is not known if the caterpillars sequester these chemicals for defense, but the caterpillars do not feed on any other plants.
Unlike other members of its subfamily, goatweed leafwings are found from the tropics into temperate zones of North America. The butterfly is capable of surviving the winter in its adult form hibernating under loose bark or other shelter. Nor do they need flowers; the adults feed on sap flowing from tree wounds, rotting fruit, and animal dung.
When caught, the butterfly makes no attempt to escape. It simply folds its wings and flops onto its side. When a predator abandons it as dead, the butterfly rapidly and erratically flies away. (Compiled from: Field Guide to North American Butterflies, Robert Michael Pyle, National Audubon Society, Alfred A. Knopf, 1994 and "Goatweed Leafwing", Jane M. Struttmann, Butterflies of North America, Northern Prairie Wildlife Research Center, USGS)
The Institute for Systematic Botany, University of South Florida has several photographs of Croton argyranthemus, a silvery croton native to the southern US. To view the photographs, click on the link:
http://www.plantatlas.usf.edu/main.asp?plantID=2097
Click on the Images tab and on the individual thumbnails to enlarge the images.
Butterflies of Wisconsin has a great photograph of goatweed leafwing with its upper wing surfaces exposed, something difficult to catch since the butterfly tends to rest with its wings closed. To view the photograph taken by Tom Lewis, click on the link:
http://www.wisconsinbutterflies.org/butterflies/species/194
The stellate trichomes that cover Croton leaves are uniquely beautiful plant structures. The Department of Botany, University of Wisconsin-Madison has a close-up of a Croton flower and an electron micrograph of the stellate trichomes. To view these photographs, click on the link:
http://www.botany.wisc.edu/croton/Pages/Project%20summary.html
Scroll down the page to view the micrograph.
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