The male Bruce Spanworm has a wingspan of approximately 1 to 1.25 inches. His forewings are light brown with dark scalloped antemedian and median lines and a dark orbicular spot. The postmedian line and terminal line are a series of dark dots. The hindwings are pale gray with a small discal spot. The female has underdeveloped wings and is flightless. The larva is bright green with 3 narrow cream-colored stripes on each side and has proportionately small prolegs. It grows to approximately one inch in length.
The frequency of occurrence is not known. The males shown here were photographed from mid to late November at Fontenelle Forest Nature Center. The adults emerge after the first frost and are active from October to December. The adults come to artificial lights.
Winter Moth is another common name for this moth. The larvae are active in late April, May and June and feed on leaves of many trees including cherry, elm, maple, oak, serviceberry and willow. The females are usually seen on tree trunks where they lay eggs singly in bark cracks. The orange eggs overwinter. During outbreak years trees can be covered with sheets of silk made by the caterpillars.
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