Wildlife Spotting

This looks like an Ichneumon Wasp, family Ichneumonidae. There are more than 5000 species in North America and I can't help you get any more specific than this. See: http://bugguide.net/node/view/150 The "butt antennae" you describe is actually its egg-laying organ, called an ovipositor. It has a sheath that covers the actual egg insertion projection and this sheath splits into two or three prongs when it lays its eggs. This is why it appears to be three antennae. They use this organ to drill into trees and logs to lay their eggs in the larvae of other insects that live in the wood.