Drought-escape behaviors of aquatic insects maybe adaptations to highly variable flow regimes characteristic of desert rivers

We document how two species of desert aquatic insects use positive rheotaxis to escape drought in desert rivers. We observed ca. 3,600 adults of the long-toed water beetle Postelichus immsi (Coleoptera: Dryopidae) crawling upstream concurrent with upstream recession of surface water in the Santa Maria River, La Paz and Mohave counties, Arizona. At the same time, we observed larvae of the gray sanddragon Progomphus borealis (Odonata: Gomphidae) burrowing and swimming upstream in large densities (690 larvae/m(2)). Both taxa moved with sufficient speed to arrive at perennial reaches of the river before being overtaken by drought.