|scientific name Ennomos subsignaria |
common name Elm Spanworm
In Alberta, restricted to southern prairie riparian woodlands.
The only Alberta record is for late May; July and August elsewhere (McGuffin 1987).
A large pale white-tan geometrid with pointed projections along the wing margins. The wings lack conspicuous markings. Tetracis cachexiata is similar, but has a straight transverse line crossing the forewing.
The larva occurs in several colour forms, all of which resemble twigs like most ennomine geometrids. Colour forms include yellow, green, brown, and nearly black (Wagner et al. 2001). McGuffin (1987) states that some colour forms may be induced by population density, with crowded larvae being dark and isolated larvae light. Eggs are laid on the undersides of twigs, where they overwinter. Like E. magnaria, larvae often spin a cocoon amongst foliage to pupate, unlike most other geometrids which pupate underground. In the East this species is sometimes abundant enough to defoliate trees (Wagner et al. 2001).
Rare in AB (1 record), but widespread and occasionally reaching pest status elsewhere.
Larvae feed on a variety of hardwood trees; the only recorded hosts which occur in Alberta include white birch, trembling aspen (Populus tremuloides) and Manitoba maple (Acer negundo) (Prentice 1963).
Southeastern Alberta east to Nova Scotia, south to FL and TX (McGuffin1987).
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