The 'cactus longhorn beetle' (''Moneilema gigas'') is a large, flightless black beetle endemic to the
Sonoran Desert. It feeds on cholla and prickly pear and is also known as a
cholla beetle. Larvae (grubs with brown heads) bore into cactus roots and stems, killing more susceptible individuals. It has a protective resemblance to the stink beetle.
Links
Cactus Longhorn Beetle Page at Friends of Saguaro National Park