These are the two most difficult species to differentiate in the Feltia genus.The most reliable method is to look at the male antennal seate. The difference can be seen here - https://www.ndsu.edu/pubweb/~gefauske/ndmoths/names/10674.htm - and these features can be seen on iNat with high image magnification, but not always.
Bugguide has a somewhat confusing description (https://bugguide.net/node/view/10466) that I no longer use. An important features to notice is the mounded orbicular spot which is not the same colour as all the costal streak.
F. subgothica has shorter antennal setae.
F. tricosa has longer setae, is darker, and looks like this.
This is only a rough guide. Due to variation and wear, it may not be possible to identify these moths visually, in which case (after Feltia jaculifera & F. herilis have been ruled out), genus Feltia Complex would be the prudent option.
Photos courtesy of CBIF.
An exceedingly variable moth. Many resemble this image, but they range in colouration from brick red to this. Main features are 7 black marks along costa, large round orbicular spot, and a fairly prominent, double AM line.
Photo courtesy of CBIF (https://www.cbif.gc.ca/SpeciesBank/spp_pages/noctuoidea/jpgs/image_e.php?image%5B%5D=110915.jpg%2CPeridroma+saucia)