Larvae of several species of fishflies in the genera Neohermes and Protochauliodes (Megaloptera: Corydalidae) live for multiple years in small California streams that are dry for extended periods of the year. Other hellgrammites in California, such as Orohermes crepusculus, are only found in perennial streams. We conducted laboratory experiments to examine the behavioral response of the hellgrammites Neohermes filicornis and Orohermes crepusculus to stream drying. Perforated plastic viewing chambers (30 cm depth, 10 cm length, 1.5 cm width) filled with gravel and sand were placed in tubs of stream water. One hellgrammite was placed in each of 16 chambers, and the water level in the tub was gradually lowered 1-2 cm per day. In response to water level lowering, Neohermes larvae often burrowed 1-3 cm into the substrate. Upon rewetting, some Neohermes larvae reemerged at the surface. Orohermes larvae did not exhibit a burrowing response to stream drying. Both species had high survival rates during the experiments, despite being out of water and not feeding for over one month. We conclude that both species possess physiological adaptations to stream drying, but only Neohermes responded behaviorally by burrowing into the streambed.