Effects of decomposition on carcass attendance in a guild of carrion-breeding flies.

Many forensically important calliphorids, sarcophagids and muscids (Diptera) oviposit or larviposit on corpses only during the early stages of decomposition, yet individuals may attend bodies throughout decay. A field study was conducted to investigate how patterns of carcass use and attendance by some fly species are affected by decomposition. Five fly traps were placed in the forest and baited with whole, fresh piglet carcasses. Piglets decomposed in traps throughout the experiment, and all were skeletonized within 6 days. Flies were trapped at both early and late decomposition stages, and the species and population structures of trap catches were compared. More flies attended carcasses early rather than late in decay. For all species, flies attending early were mainly gravid females, but few gravid females attended late in decay. No females ovi- or larviposited late in decay, whereas females of all fly species deposited offspring early in decay. The number of males trapped of each species correlated positively with the number of females with eggs at early development stages. Observations were made of fly predation by European wasps Vespula germanica Fabricius (Hymenoptera, Vespidae) and jumper ants Myrmecia pilosula Smith (Hymenoptera, Formicidae) throughout the experiment. There was a higher risk for smaller fly species of being killed following predator attack. Ants and wasps attacked smaller fly species, whereas only wasps attacked larger fly species.