This study examines the soil hydrological and erosional effects of ant mounds during summer and winter conditions following a wildfire in scrub terrain in eastern Spain. Forty rainfall simulations (1 m2 plots, 1 h duration, 78 mm h−1 intensity) were carried out over plots with mounds (n = 20) and mound-free control plots (n = 20) in August 2002, and repeated in December. By winter, some of the mound material had been removed and some vegetation regrowth occurred. Overall, mound presence increased soil erodibility in summer and winter due to the availability of highly erodible mound material. However, mound plots showed higher mean overland flow rates in summer (10·1 vs 6·9% for control plots) but lower rates in winter (59·3 vs 74·4% for control plots). This reversal is suggested to be caused by (i) post-fire changes in ground cover and (ii) seasonal differences in antecedent soil moisture. First, immediately after burning, an absorbent ash layer covered much of the soil surface, but this was partially masked by less permeable mound material, reducing infiltration on mound plots. By winter, the ash layer had been largely removed and ash particles clogged soil surface pores, reducing overall infiltration on control plots compared to mound plots. Second, during summer, the dry soil underneath the absorbent ash cover has a high infiltration capacity. In winter, soils are near saturation, resulting in a much greater runoff coefficient. Under these wet soil conditions, the presence of macropores (i.e. nest entrances) becomes important, reducing overland flow in mound plots. Copyright © 2010 John Wiley & Sons, Ltd.