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Ottawa (Dunrobin), ON Canada
16 June 2003 9:32PM EDT (top)
3 July 2007 10:39PM EDT (center)
28 June 2007 12:33AM EDT (bottom left)
26 May 2003 11:34PM EDT (bottom right)
Biston betularia, also known as the Pepper-and-Salt
Geometer or (in the United Kingdom) the Peppered Moth, has been the subject of
considerable study (and controversy) over the possibility of its being an
example of natural selection at work, some having asserted that grime on
buildings accumulated during the Industrial Revolution in England led to a shift
toward darker-colored (melanic) specimens becoming the dominant form in
industrial areas. McGuffin indicates that the North American subspecies is
cognataria (McGuffin, W.C., "Guide to the Geometridae of Canada (Lepidoptera),
II. Subfamily Ennominae. 2", Memoirs of the Entomological
Society of Canada, no. 101, Ottawa, 1977).
The forewing of Biston betularia is light gray,
suffused to varying degrees with gray-brown to blackish. The fine blackish
antemedial line bends inward shortly above the inner margin, and is preceded by
a dark gray-brown shade. The middle of the wing is crossed by a dark gray
medial shade, often interrupted or incomplete, thickest close to the costa, and
the median is often conspicuously peppered with dark gray dots. The fine
blackish postmedial line bulges sharply outward a short distance below the costa,
and is usually followed by a gray-brown shade. A pale, somewhat
irregularly diffuse subterminal line is sometimes evident. The forewing
fringe is checkered dark and light gray. The hindwing is similar, but
without an antemedial line. The abdomen is much stouter than is usual
among geometrid moths, often crossed by a color pattern similar to that of the
forewings. McGuffin (1977) indicates a wingspan of 40 to 60 mm.
According to Handfield (1999), the larva of Biston betularia
cognataria feeds primarily on willow and birch, but also on a wider variety
of trees, shrubs and other plants including alder, dogwood, maple, poplar,
cherry, gooseberry, strawberry. buffalo berry, elm, etc. For my general
area, Handfield (1999) indicates an adult flight season from about mid-May to
the end of July, sometimes with a rare partial second generation flying from
early August to about mid-September.
My records to date for Biston betularia (each date
representing "the night of") are in the table below: |
