The arrival of tender spring vegetation in the desert is a signal for the arrival of hungry opportunists. I saw thousands of white-lined sphinx moth caterpillars (Hyles lineata) on the march across the Cottonwood Canyon bajada at Joshua Tree. They would strip a plant bare, and then move on. I had never seen the black-striped western morph before. Back east we prefer our H. lineata caterpillars camouflaged green, to better blend in with the tomato plants they are eating.