Ottawa (Dunrobin), ON Canada

11 July 2005   10:11PM EST  (top)
25 July 2005   11:40PM EST  (center left)
14 May 2004   11:11PM EST  (center right)
31 May 2005   11:00 to 11:01PM EST  (bottom left, center and right)
The three photos at bottom are of the same specimen. 

Members of the Geometrinae subfamily of Geometridae are often called the Emeralds, or emerald moths, because so many of the species are green in color.  Nemoria bistriaria is one of eight species of Emerald recorded from the Ottawa area (J.D. Lafontaine, pers. comm., 2001), of which six are illustrated on this web site.  Distinguishing between similar species in this group is often problematic, and in checking my identifications and revising my web pages for this group of moths, I have relied heavily on the work of the late Dr. Douglas C. Ferguson (Ferguson, Douglas C., in Dominick, R.B., et al., 1985, The Moths of America North of Mexico, Fasc. 18.1, Geometroidea: Geometridae (in part)).

The Nemoria bistriaria specimens illustrated above are all, I believe, of the subspecies siccifolia, which Ferguson (1985) describes as a northern form of the species occurring approximately from Pennsylvania to southern Quebec and Ontario, and one in which the spring generation is predominantly green in color, unlike some other Nemoria species.  Distinguishing Nemoria bistriaria siccifolia from similar species of Nemoria is facilitated by the presence of a red terminal line on the wings, as Ferguson also notes that Nemoria bistriaria siccifolia is the only species of Nemoria with a red terminal line throughout all or nearly all of its range.

The wings of Nemoria bistriaria siccifolia are green, with white antemedial and postmedial lines sharply defined on both forewing and hindwing.  The am and pm lines are somewhat variable in shape and spacing, as can be seen in the photos above.  A thin red terminal line precedes the whitish fringe, which often has pink streaks at the ends of the veins, and which is sometimes suffused with pink as in the specimen at center right above.  The underside of the wing is paler.   The abdomen has several cream-colored spots encircled in a reddish color; in the specimens I have photographed, these marks are generally somewhat diffuse, rather than sharp and well-defined.  Ferguson (1985) indicates a wing length ranging from 10 to 12 mm in males, and from 11 to 13 mm in females.

On several occasions, I have observed specimens with pinkish shading in the median adjacent to the am and pm lines, as in the last specimen pictured above.  To date, I have found no references in the literature to such shading, but have assumed these specimens to be Nemoria bistriaria siccifolia on the basis of other characteristics of their appearance.  Any information on this apparent variant would be appreciated.  

Ferguson (1985) indicates that the primary host plant for Nemoria bistriaria siccifolia is white oak, the presence of which may account for the relative abundance of this species at my location.  According to Handfield (1999), this species has two generations per year, with adult flight seasons from early May to early June, and from early July to early August in my general area.

My records to date for Nemoria bistriaria siccifolia (each date representing "the night of") are in the table below: