Friday, May 4, 2012

Butterfly of the Week

Southern Cloudywing

Thorybes bathyllus (Smith 1797)
Status: Infrequent breeding resident
Flight: Most likely three broods, with adults flying from early May to mid August. It appears to be most often encountered in early May, from mid June to early July, and in mid August.
Distinguishing features: This species and T. pylades are quite similar. Both are brown with white spots on the upper fore wing and have a series of dark brown markings on the lower hind wing. In T. bathyllus, the dorsal white spots are larger and shaped like an hourglass, the wing fringes tend to be paler, and the dark brown hind-wings bands appear solid rather than hollow. Additionally, males lack the costal fold. Wingspan: 3.5-4 cm.
Distribution and habitat: Map 47. The Southern Cloudywing has been observed sporadically across the southern two-thirds of Iowa, with outlying populations also occurring in the Paleozoic Plateau. It is most frequently encountered in xeric grasslands, including Loess Hills prairies, sand prairies, limestone and sandstone glades, and occasionally in old fields.
Natural history: The larvae of this species favor wild beans and goat's rue, which are most often found in dry, open, and sandy places. One of the most impressive Southern Cloudywing populations occurs on the state's largest goat's-rue population at the Big Sand Preserve in Louisa County. Goat's-rue is quite uncommon in the state and essentially limited to the southeast so it is likely that wild bean constitutes the more frequent larval host.
Questions: How often do T. bathyllus and T. pylades coexist? When both wild bean and goat's-rue are present, which is the preferred larval host?

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