We were just heading out for our second full day when this beauty alighted upon a tree trunk right in front me. This beast was gigantic, easily 5-6 cm from head to abdomen, with an ovipositor almost twice as long.

After looking around, I think this was a Giant Ichneumon in the genus Megarhyssa. BugGuide and Nearctica agree on the list of species that occur on this continent, and the pics on BugGuide lead me to believe this is Megarhyssa macrurus.