ABSTRACT: Animals living in intertidal habitats experience high temperatures and low humidity during emersion that represent extreme deviations from those experienced during immersion; some use behaviour to ameliorate these stressors. We made in situ observations of 3 behaviours displayed by the Pacific intertidal snail Littorina subrotundata on 3 exposed rocky intertidal shores in the northeast Pacific: microhabitat selection, activity level, and conspecific aggregation. We hypothesized that these behaviours might be altered in response to temperature and/or humidity at a particular time during tidal emersion. We used the Akaike information criterion to compare a set of models for each of the 3 behaviours that included combinations of substrate temperature (T_s), vapour pressure deficit (VPD) (which encompasses humidity), emersion time, snail shell width (Size), and study site (Site) as the independent variables. The best supported model of microhabitat selection in the summers of 2011 and 2012 used only the independent variables Site and Size. The best supported model of activity included both T_s and VPD in 2011 but included only T_s in 2012; increased T_s resulted in decreased activity. None of the models in the set explained much of the variance in conspecific aggregation. We conclude an alternate cue for microhabitat selection is likely in this system and suggest that biogenic refuges created by barnacles are a likely driver. Our findings also suggest that thermal stress during emersion is the primary cue that informs the snails to reduce their activity.