|scientific name Biston betularia |
common name Pepper & Salt Geometer
Widespread in deciduous and mixedwood forests, parklands and shrublands.
Flies from May to July, peaking in mid-June.
A large heavy-bodied geometrid. Wings light grey with black speckling and a well-defined black AM and PM line. Lycia ursaria has a less pointed forewing apex and lacks the black-on-white speckled appearance; Nacophora quernaria is similar, but has yellowish-ochre shading in the subterminal area which is absent in B. betularia. This species also occurs in the Palaearctic region, and North American populations are assigned to subspecies cognataria (Gn.) by some.
A detailed description of the immature stages is given by McGuffin (1977). The eggs are laid in bark crevices and old alder catkins, and hatch in about 12 days. Over 600 eggs may be laid by a single female over the course of several weeks. Larvae are twig mimics, and pupation occurs in the soil prior to the onset of winter (McGuffin 1977).
The increase in frequency of the melanic form of B. betularia in conjunction with industrial pollution in Great Britain is often cited as a classic example of direct evidence of natural selection; tree trunks blackened by air pollution favored the survival of the black form, which were supposedly less visible to birds than the typical pale form. Following air quality legislation, the frequency of the black form has again declined, both in Europe and the industrial northern Great Lakes region in North America (Grant & Wiseman 2002).
Common and widespread; not of concern.
Larvae feed on a wide range of trees and shrubs (over 50 species reported), and were most often collected from willow (Salix spp.), white birch (Betula papyrifera), alder (Alnus spp.), larch (Larix laricina) poplars (Populus spp.), and Manitboa Maple (Acer negundo) by the Forest Insect and Disease Survey (Prentice 1963).
Occurs from coast to coast across Canada, from Fort Simpson NWT south to North Carolina and Chihuahua, MEX (McGuffin 1977).
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