Not sure how closely your captives follow with the wild populations in when they are at what stage. The mid-winter adult might imply a population normally overwintering as nymphs and maturing in spring, which would imply G. veletis to me (further south there would be a several more species to choose from). However, if they are way off of their natural cycle, this might not mean much. Otherwise, I don't know how to tell G. pennsylvanicus from G. veletis (there may be a way that I'm not aware of). I think (in my experience) G. pennsylvanicus are more likely to have big heads and G. veletis to have long wings, but that really doesn't help much, since neither character is constant, and both probably vary from place to place. Identifying Field Crickets without observations and recordings of the songs really is difficult too. In some you have things like different counts of teeth on the files of male's wings, or ovipositors are longer or shorter with differing little projections at the tips; one or two can even be identified by coloring. But, I don't think that helps with these two.

Moved from Field Crickets.