Several weeks ago while strolling around Castle Crags State Park near Mt. Shasta I saw a male Polyphylla frantically exploring a small spot of trail. It would fly a few inches up into the air, circle around, and then land again. From there it would rapidly scurry about until after a few moments, it began digging. Quickly it excavated a female Polyphylla from about an inch under the surface. After maneuvering the female into an appropriate position, they began mating.

I've tried ID'ing them using Robert Young's monograph on the genus, but am having a great deal of trouble, especially with regards to the features of the pronotum setae, the pattern of the elytral vittae, and their base colors, I believe they are either P. decemlineata, P. nigra, or P. crinita, but I'm just not familiar enough with the genus to distinguish the subtle features that separate these species.