Archimylacris lived on the warm swampyforest floors of North America and Europe 300 million years ago, in the Late Carboniferous times. Like modern cockroaches, this insect had a large head shield with long curved antennae, or feelers, and folded wings. To a modern observer, it would likely appear as moderate-size cockroaches, with "tails" (an ovipositors) in the females. Presumably their habits would be cockroach-like too, scurrying along the undergrowth eating anything edible, possibly falling prey to labyrinthodontamphibians and very early reptiles. The average length of Archimylacris species was 2–3 cm.