I'm so glad to have found this post! I rescued one of these little fellows in the middle of the Tempe Town Lake while I was paddle boarding. It stayed on my board with me until I made it to shore and I let him off in a tree. I had NO IDEA what he was or if he was dangerous so I kept him on the other side of the board... Thank goodness. I have a little bit clearer photos of it, but I don't know if I'm able if I'm able to add them here or not.

Either way, that is for the post!

Yes, these are "locally common" insects that are sometimes abundant in a small area, for a short period of time. You could probably go for miles before you see another one, but there would be many....Yes, they are poisonous. They secrete a potent defensive chemical (cantharidin) from their body joints if squeezed. The chemical can raise painful, scarring blisters on sensitive skin. Ingested, the insect can be lethal, so keep curious kids from sampling one. Same goes for pets. I believe the larvae of these beetles are parasitic on other insects, but I'm not positive. Adults will eat foliage, and sometimes cause severe damage to plants in areas where the beetles are numerous.