Coprophagous insect communities play a critical role in the decomposition of vertebrate dung and provide ecosystem
functions fundamental to modern agriculture. While the ecology of dung beetles is rather well understood, niche differentiation in
coprophagous fl ies is poorly studied. Sepsid fl ies (Diptera: Sepsidae) are a vital part of the European community of coprophages,
with 6–7 widespread species of Sepsis often found co-occurring in the same pasture. To advance our ecological understanding of
the mechanisms that enable species to coexist, we investigated the oviposition preferences and larval performance of 7 common
species of Sepsis in the dung of different large domestic and wild mammals. Substrate preferences and subsequent performance
of larvae in laboratory experiments did not vary greatly. All species did very well on cow dung, the most common substrate in
Central Europe, but also on dung of horse and wild boar. In contrast, fl ies did not prefer or grow well in dung of red and roe deer,
two of the most common wild vertebrates. Thus there were only minor differences among the species tested along the specialistgeneralist (dung) gradient, indicating that differences in the choice of oviposition sites by the adults of the different fl y species
and larval performance do not constitute a major axis of ecological differentiation. Nevertheless, there was a positive correlation
between substrate choice and larval performance indicating the preference of gravid females for particular oviposition sites is
adaptive. We conclude that sepsids are common in Europe because they are well adapted to the dung of herbivorous livestock
rather than wild animals. Nevertheless, specialization on particular types of dung does not defi ne the niche of Sepsis dung fl ies
and hence plays a minor role in mediating their species diversity.