Thursday, April 26, 2007

Southern pearly eyes

Weighing in as the third most common butterfly in the woods this spring (#1 pearl crescent, #2 zebra swallowtail) is the Southern pearly eye. If you enlarge the picture, you can see a small pearl white spot in the center of each of the four spots on the forewing. In Missouri, as in everywhere else in its range, the Southern pearly eye only lives where the larval host plant, giant cane, grows. Aside from counties in the embayment, counties along the Current River drainage and at the Missouri-Arkansas border also harbor cane populations.

Southern pearly eyes belong to the family Satyridae, which includes ringlets, wood nymphs and satyrs. Butterflies of this family do not feed on flower nectar but gain sustenance from tree sap, rotting fruit, carrion and manure.

Eggs of the Southern pearly eye are laid singly on or near cane. The larva has the ability to hibernate during the winter, though they breed from April to November. There are two other butterflies who depend on cane for their life cycle, the Creole pearly eye and the southern swamp skipper. Research in the past 20 years determined that the now extinct Bachman's warbler depended on cane obligate invertebrates like the pearly eye. Young birds were fed the Southern pearly eye caterpillars, but with the conversion of canebrakes to cropland, the cane invertebrates also disappeared. And without the invertebrates, so goes the bird.

The now rare Swainson's warbler is headed in the same direction as the Bachman's warbler. Swainson's warblers, too, depend on the caterpillars to feed their young. Luckily, several agencies are spearheading efforts to restore cane to southeast Missouri with the conservation of the Swainson's warbler in mind.

A close relative of the Southern pearly eye is the common eastern species, the pearly eye. This butterfly lives in moist woods from Arkansas to Canada and east to the Atlantic. The pearly eye feeds on grasses other than cane. The most distinguishable difference between the two is the color of the antennal knobs: the Southern pearly eye has orange knobs while the common pearly eye has orange knobs outlined in black. A digital camera with a good zoom lens helps to determine the species, as does offering the butterflies an intoxicating slurry of beer, bananas and yeast. They sit still for several minutes at a time on bait stations, essentially drunk on the fermented fruit.

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