One of the most unusual blister beetle genera in the United States is Cysteodemus. It occurs in the desserts of the Southwest. There are only two species, C. armatus and C. wislizeni and both look like inflated and highly sculptured versions of what your more typical blister beetle looks like. Werner, Ens and Parker (in the Meloidae of Arizona (Technical Bulletin 175 (1966) of the University of Arizona Agricultural Experiment Station)) write that they sometimes look "more like a Christmas ornament than an insect when ... seen on its food plant". Their inflated appearance certainly makes them look bigger than they really are (even though they're only half an inch long). Underneath the inflated wing-covers there is mostly air and the flight wings are missing.
The two species are fairly easy to tell apart. Cysteodemus armatus is black and has a more sculptured back. Cysteodemus wislizeni is metallic purple or bluish and has a finer and a more pitted sculpturing on the back. The best place to find these fascinating beetles is in the deserts of Arizona, California and New Mexico at night with a flashlight, where they crawl along the sand. One beetle enthusiast claims that they have a glow about them if spotted with a UV flashlight.