I recently saw this beetle while on a trip in central Texas, USA (in a rural area just before sundown). The body was about 2-3 inches long (compare to nearby chair leg and floorboards) and had a long body. It was very vivid green, and its upper legs were very bright orange (which made me wonder if this is aposematism). Its antennae had very uniform half-circle arcs (instead of the uneven parabolic shape often seen in cockroaches and similar common insects) and didn't seem to bend besides being rotated ~5 degrees up and down.
It carried itself pretty high off the ground, perhaps half an inch between the belly and ground-level. It seemed to move fairly fast, but not as fast as a cockroach. It didn't fly in the few minutes I observed, and didn't seem like it could fly since the shell appeared solid, but I might have mistaken well-fitting sheaths for fused ones.
What is the most likely species? Is it poisonous?