The larval dynamics of an Aphodius assemblage in southern Ireland were monitored over a full year's activity period (March-October). This is, to our knowledge, the first published analysis of larval dynamics across an entire assemblage of north temperate Aphodius dung beetles. Total pitfall catches of adults were strongly correlated with total larval numbers in 20 day old dung pats, but the relative species abundances of adults in pitfall catches and of larvae in dung pats did not correspond closely. In late summer rapid decomposition of dung pars occurred, associated with relatively low temperatures, high rainfall, high earthworm biomass and colonisation of dung pats by the large paracoprid dung beetle, Geotrupes spiniger. This decomposition was so fast that it is likely that no Aphodius larvae completed their development in these dung pats, although some A. rufipes larvae survived by kleptoparasitising G. spiniger nests. Asymmetric competition with earthworms, and interactions with G. Spiniger are likely to have important effects on the dynamics of Aphodius larval assemblages in southern Ireland.