Inflated Beetles

When we arrived at Red Rock Canyon State Park, it was nearly midday and the temperature was 89 degrees, just right for a stroll among the crumbling towers, rocks and gravelly dry streambed. While doing that we found a couple of these beetles running around in the gravel seeking plants which they then ran up then down, pausing to nibble at selected somethings now and then. They turn out to be Cysteodemus armatus, inflated blister beetles also known as desert spider beetle. Notice that these display two different color patterns; the species comes in several variations but I didn't know that at the time I was observing them and thought, well, I didn't know what to think really but figured I'd find out later as long as I managed to get a few decent pictures. Which wasn't too easy given the speed they were running and the possibility of rattlesnakes lurking under the rocks I was trying not to trip over.

Aside from their weird looks, these beetles seem rather interesting: They are flightless; there is a dead air space under the pock-marked elytra which functions as insulation from the heat; they are most active in the heat of the day; their hemolymph contains a toxin that will cause skin irritations; they have a hypermetamorphic life cycle, wherein the larvae pass through various stages with different morphology and behaviors; the larvae are parasitoids (on bees?) while the adults eat wildflowers that appear briefly in spring; and these beetles enjoy the finer things in life as they live in the Mojave and Colorado deserts in CA, AZ and NV. Oh, and, none of the sources I read mention this but as the beetles ran they emitted a very theatrical swishing or scrapey sound which reminded me of a movie (maybe it was Disney's Living Desert, remember that?) where the sounds made by small desert creatuers as they scurried were made hyper-real by movie magic. Except this was real.

Inflated blister beetle, I was glad to make your curious acquaintance this spring.