Definite Tussock and White-marked Tussock are flying now (September) in our area. Here's how to tell them apart:
The moth on the left is Orgyia definata and the one on the
right is O. leucostigma. Because the MPG site had no useful info and the photos in Beadle and Leckie
leave something to be desired, IMHO. I dug out Covell and read his
descriptions of the two species. Here’s what I found:
In both species, females are wingless. The descriptions are
of males.
O. definata: “FW dark grayish brown, with relatively sharp
black markings in the upper st. area. Note thin, black costal patch with black
and gray streaks below it, near FW apex. St. line usually sharp, accented by
white spot near bottom.”
O. leucostigma: “Similar to Definite Tussock Moth. . . Wings
usually grayer in [male] of this species; median area usually paler. Blackish
patch near apex smaller, with no light streaks below it. White spot accentuates
lower st. line as in [male] Definite Tussock Moth.”
I would add that Covell did his descriptions from pinned
specimens. Therefore, the forewing costa (leading edge) is “up.”
