Right family and subfamily, but it is not Prionus. This specimen is a female Derobrachus geminatus, the "palo verde root borer." They are very common, and of little consequence to anyone but motorcyclists (well, I wouldn't want to collide with one at high speed, anyway:-). The adults will be gone in a matter of weeks.

no, wouldn't want to collide with one while on a motorcycle...especially since AZ doesn't have a helmet law...to quote a favorite movie (but wrong context) "you'll shoot your eye out". Thanks for the info...the kids still want to put a leash on it!!

OK, YUCK!!
are they dangerous? poisonous? what do they eat?
should I be concerned with two small children or should we put a leash on one and give it a name if we find one live??
Thanks for your quick reply!!
Judy

but it could give you a good hard pinch with its mandibles, so young kids shouldn't handle it.

Adult prionids don't seem interested in eating, nor do they live more than a few weeks. The prionid larva gets fat on wood, turns into a pupa, and an adult emerges a few weeks later with a very plump abdomen. When this recedes in a week or two and the beetle is able to fly, it has only two things in mind -- finding a mate and procreating. The male dies a short while after mating and the female dies soon after laying eggs.

By the way, while there is usually an exception to any rule, I know of no beetle with a poisonous bite. Many beetles are poisonous to eat and some, such as blister beetles, exude toxins that cause skin irritations. The longhorned beetles, including prionids, are not big on toxins.