Identifying insects (and other critters) is a reasonable method most of the time, but sometimes is impossible. An example is the Geometer moth genus Hydriomena. There are probably several species in our area, but the color and patterns on the wings are highly variable and cannot be used safely to distinguish species. Last July I photographed a Zale that I was unable to identify at the time. This morning (April 23), I was recording the appearance of two species of Zale when I noticed an "unidentified" folder and took a peak. The moth was very dark at normal exposure/brighness and the pattern didn't show.
The above photo is a reduced version of the original. You can see a bit of the pattern in the wings but not much. So, I adjusted the brightness of the photo until the patter appeared. The result was a confirmed ID of
, Green-dusted Zale.
I spotted an
recently. The general color pattern was correct for the species, but the field guides indicate that the pattern on the wings is useless because it's so variable. In other words, pretty but useless.
However, unlike other similar Orthosia species, males of O. rubescens have bipectinate antennae (bristles on both sides). As you can see in the photo below, the antenna is clearly bipectinate and therefore the ID is proven.