This is a firefly larva and matches pics on BugGuide of the Black Firefly (Lucidota atra); I've also found pupae of that species (which glow!) in leaf litter a couple of meters from here and seen adults as well. Found while digging up the remaining rotten roots of the elderly dogwood uprooted during the October snowstorm, but unable to ascertain whether they came from the tree or from leaf litter. 16 mm.