Abstract1Analysis of insect ‘death assemblages’ from ancient natural and anthropogenic deposits can provide valuable information about conditions in the past but the theoretical basis of such investigations is weak, especially with respect to the quantification of habitats on archaeological sites.2Evidence is presented for the existence of a transported component, termed ‘background fauna’, in death assemblages, as well as the remains of insects derived from the immediate surroundings.3The background component is derived principally from airborne insects and from bird droppings and may seriously detract from the accuracy of reconstructions of past ecological conditions. Factors affecting its relative importance are discussed.4As well as including species from distant habitats, the background fauna may be biased in favour of species from temporary habitats.5Some solutions to the problems presented by the background fauna are discussed. A high proportion of a species or ecological group will usually be evidence that its habitat existed near to the deposit enclosing the fauna, although there may be exceptions.6The structure of the background rain of insects has probably altered with changes in town and countryside brought about by man. Attempts to recognize background fauna in ancient assemblages must take account of this.7Many ancient assemblages, especially if small, will give no useful ecological info