Ottawa (Dunrobin), ON Canada

13 June 2005   9:37PM EST  (top left)  (female)
13 June 2005   10:27PM EST  (top right)  (male)
17 June 2004   11:33PM EST  (second row)  (male)
13 June 2005   9:40PM EST  (third row, left)  (female)
29 June 2001   12:25AM EST  (third row, right)  (male)
13 June 2005   9:16PM EST  (bottom left)  (female)
13 June 2005   10:27PM EST  (bottom right)  (male)
The photos at top left, third row left and bottom left are all of the same female specimen.  The photos at top right and bottom right are both of the same male specimen.

Prionoxystus robiniae is one of three members of the Cossidae family that have been recorded from the Ottawa area (J.D. Lafontaine, pers. comm., 2001), two of which are illustrated on this web site.  The Cossidae are grouped with the micromoths in the classification of lepidoptera, which is based on characteristics other than size; however, in this case, "micromoth" is a misnomer for species that may have a wingspan up to 8.5 cm!

This species exhibits sexual dimorphism, the male being significantly smaller than the female (see the two photos at bottom) and having a colored band on the hindwing.

Both male and female Prionoxystus robiniae have translucent wings, mottled in gray and near black.  The forewing of the male is somewhat darker and less mottled than in the female, but there is some variation from one individual to another. The general appearance of the wing is suggestive of black netting over a gray and black background.  The hindwing of the male is near-black, with a wide, yellow to deep orange band along the outer margin.  The hindwing of the female is dark smoky gray without any colored band.  Both sexes have heavy bodies, with a light gray head and thorax.  According to Covell (1984), the wingspan ranges from 4.3 to 8.5 cm, the female being larger.

According to Handfield (1999), the larva of Prionoxystus robiniae, also known as Carpenterworm, tunnels in the trunks and branches of various trees, including poplar, willow, locust, oak, elm and sugar maple.  For my general area, he indicates an adult flight season from late May nearly to mid-July.  The life cycle of this species takes three to four years to complete (Covell, 1984).  In my experience, Prionoxystus robiniae is a noisy flyer, making a loud buzzing sound as it circles under the ultraviolet light.

My records to date for Prionoxystus robiniae (each date representing "the night of") are in the table below: