Germination of primary and secondary conidia of 33 strains (12 spp.) of co-occurring Conidiobolus and Basidiobolus from three closely adjacent managed habitats was studied in relation to general nutrient level, water activity of substratrum, light and temperature. A further 26 strains (16 spp.) derived from culture collections, and including insect pathogens and saprotrophs, were also compared. Nutrient levels triggering germ-tube formation differed widely amongst strains ; capilliconidial strains and/or presumptive pathogens usually had a low threshold. Successive generations of globose replicative conidia formed alternative conidial forms in increasing proportions. Water activity (aw) strong influenced development of non-globose conidial forms (microconidia, capilliconidia and actively discharged elongate conidia). Profiles of response to nutrients, aw, temperature and light differed between strains (and species) and the comparison represents a first stage in determining niche differentiation, including the putative interactions of these common fungi with litter invertebrates.