Compton Tortoiseshell (Nymphalis i-album)

Resident Common Conservation Status Vermont S5 Global G5 North American Range Southeast Alaska and Canada south in the mountains to Montana and Wyoming; east across southern Canada and the northern United States to New England; south to North Carolina and Missouri. Rare migrants to Newfoundland, Nebraska, and Florida. Also found in temperate Eurasia.

A holarctic species, Compton Tortoiseshell (often mistakenly called Compton’s) has one of the longest life spans of any butterfly in Vermont, about 10 months. Overwintering adults often huddle together in large aggregations to survive the cold. This butterfly has a rapid, dashing flight, but it occasionally alights on observers. Males perch to await females. Eggs are laid in clumps on hostplants, and caterpillars feed communally.

Identification

Upperside is orange-brown with darker wing bases and black spots; a single white spot on leading edge of each wing. Underside is mottled gray and brown, with dark bases and borders; hindwing with small white V at outer end of cell.

Flight

Overwintering adults emerge in spring. Summer generation begins to fly in late June and then aestivates until fall and finally overwintering. Some may migrate south. Extreme dates: 19 March 2005 in Rupert (M. Pfeiffer) and 31 October 2006 in Rupert (D. Rolnick).

Distribution and Habitat

The Compton Tortoiseshell is found throughout Vermont, though not in abundance. They are northern climate specialists and most often make their homes in moist forests, either conifer or deciduous. They are usually seen on trails and roadsides. Caterpillars have various host plants including Cottonwood (Populus), Willows (Salix), and Gray Birch (Betula populifolia). It has been noted that adults will nectar from Willows, but more often prefer to feed on tree sap, rotting fruit, or dung.

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