Friday, January 16, 2015

Lighting and Butterfly Identification

Many butterflies are only identified by the underwing color and pattern. Hopefully the butterfly cooperates and shows the wing surface necessary for identification. Fortunately, Commas or Anglewings can be identified either by the upper or underwing. They are separated easily from other butterfly species by the whitish silver "comma" mark on the underwing. There are four species I regularly encounter in western Montana: Satyr, Green, Oreas and Hoary. The underwing coloration, in general and subject to variation, of each respectively is: buffy brown, dark brown, blackish brown and grey.

The position of the wing in relation to the sun is critical for "true coloration", ergo proper identification. Remember coloration of butterflies (and birds too) observed may or is determined by light striking actual colored pigment or by absorption/reflection by the wing scales. And scales cover a transparent membrane. The three photos below illustrate wing coloration of a Hoary Comma (Polygonia gracilis) nectaring on Rabbitbrush under different light aspects (same day/same place).

Note the reddish brown underwing coloration of the most immediate photo below. For sure an artifact of backlighting, the wings are open enough for direct light to strike the upperwing. As a consequence the orange color suffuses the underwing. The second photo below captures the butterfly with its wings partially open negating backlighting, but introducing a shading factor. The underwing is not getting direct lighting and is likely darker than it really is. The third photo reveals the true underwing color, grey...diagnostic for a Hoary Comma.

Again, lighting is very important for identification by sight or photograph. This situation crops up on a regular basis even when aware and compensation (keeping the sun to your back...if possible) is attempted. All is not lost because many less-than-ideal looks/photos will still have enough colors and features to id, if that is one of your goals. Study your field guides now...April/May is not far away to test your skills :-)

Wings Folded Open "Backlighting" Underwing

Wings Partially Open Shading Underwing

Wings Closed, Underwing Exposed to Direct Light