But the AM and PM lines don't meet, isn't that the key for C. erechtea?

but in practice the "touching" thing is a very unreliable trait (more a rule of thumb). None of those "key" characters are constant and totally reliable in these particular Looper moths, and they have to be taken in combination, with a grain of salt, and the overall pattern has to be evaluated.

The only sure way to tell them apart with 100% certainty is male genitalia (and I don't know if that is truly 100% either, since I wouldn't even be surprised if they hybridize). I need to refresh myself on the details of the genitalia, since I haven't disected one in about 35 years, but it doesn't work for photos anyway.

The two species do tend to look fairly consistently different though, with a few occasional individuals that are basically impossible to identify. It is usually only the upper front wings that show in photos, and the thing that is most important to look at is the overall shape of the markings. I'm fairly confident that most of the ones on BugGuide are correctly identified (I also expect that a few probably aren't); so, if you pull up the images page and browse the thumbnails, you should be able to get a "feel" for the difference in appearance, and develop a bit of gestalt for telling them apart. Every pattern element averages a little different in the two species, and adds up to an overall pattern difference, even if in some individuals some elements look the same. The two main dark(ish) bands across the wings are a good place to start, and I'll stick with them here. The more basal of the two usually reaches clear across the wing and broadens out like a boot near the inner margin of the wing. In this species it is usually quite broad, often somewhat subdivided with parts faded (or not), and is usually quite irregular along the outer edge, commonly touching the second band not only at the tip, but also in the middle. It almost always broadly reaches the inner margin of the wing leaving the end wide and squared off. The outer band is narrower, but usually also irregular on the inner edge, making the gap between the two bands usually quite uneven in shape. The two bands often do touch near the inner margin and sometime merge completely there, but often they don't touch at all (but are almost always close).

In the other species these bands are usually noiceably narrower, and more even in shape, with the wider more basal one often not reaching the inner wing margin at all, and usually rounded off there. The wider band is not as likely to be broken or partly faded. Both bands are straiter on the apposing sides, and rarely do they even come close to touching. The space between them is usually much more even (and more well defined) in shape.

I'll leave it at that, but there are other traits as well.

It is also true that both species vary somewhat regionally, and are easier to tell apart in some regions than others. It seems to me that they are particularly difficult in the Northeast.

Thank-you David, that is very helpful!

Thank-you Lisa, that does look like a good match. Only a handful of states and provinces without records of this one, but WV is one of the ones lacking on the BugGuide map.