(Brattleboro, VT) 2 of this insect found together in bark of a tree stump while camping in southern VT. One black, with a hard, beetle like head, caterpillar like body & the other, beige w/ brown markings, had recently shed it’s outer black casing …reveling a softer head (with pinchers) but now with antennae & new wings. They were about the length of my middle finger. Could they be stages of a giant moth type perhaps? Please LMK if you know what these are, we’re quite curious!
Your photos look like they are fishfly larvae…not sure why you found them in the bark of a tree trunk unless that trunk was in or near the water …was it? The mature larvae crawl out of the water( up to 50′) to pupate, so that is perhaps why you found them in the trunk.
The dark larva has not pupated, but as you guessed the light colored one has.
Fishflies and Dobsonflies look a lot alike so yours may be dobsonfly larvae, they are the same family but different genus.