One of the pools with the tadpoles was supporting this giant water bug. This insect was about an inch long, and I think that it may be Abedus herberti, given what I’m seeing on the blog written by Arizona entomologist "Dragonfly Woman." Check for yourself .
From what the Dragonfly Woman says, I’d lay a hunch that this giant water bug is preying on the tadpoles in the pool, an example of an unsettling invertebrate-feeding-on-vertebrate relationship. Unsettling to us vertebrates, at least, since it strikes us as an inversion of how the food chain is supposed to work.