Many similar sepsid dung fly species coexist on European pastures, contradicting conventional wisdom of niche theory and competitive exclusion. We hypothesized that closely-related sepsid species on the same pasture in Switzerland avoid each other by having different spatio-temporal microhabitat niche preferences, thus enabling coexistence. A thermal racetrack experiment in the laboratory tested the thermal preferences of males and females of 9 coexisting temperate Sepsis dung fly species from Switzerland at two acclimation temperatures. The sepsid species investigated here showed no strong differences in thermal preferences. Flies of all species preferred to settle at cooler temperatures, and otherwise utilized the entire range (from 12°C to 30°C) offered for their activities. This was the case for both sexes, and also for both acclimation temperatures (18°C, 24°C). Our findings suggest that physiological thermal adaptation or acclimation is not an important mechanism by which adult sepsid flies avoid interspecific competition. Our experiment supports previous findings of widespread sepsid flies lacking local adaptation but high phenotypic plasticity, again highlighting the necessity of experimentally assessing putative biological mechanisms facilitating coexistence.