Pricklypear Borer Caterpillar

Description:

I saw two of these bright blue caterpillars (or grubs?), each about 1.5 inches long, within 50 yards of each other. I've never seen another one before or since. They were walking on the ground.

Habitat:

A sage plain near Navajo Dam, NM.

Notes:

I did not see these caterpillars on prickly pear, but it is present in the area. See a couple of additional photos at http://textless.tumblr.com/post/12342061....