The human DNA content in artifacts deposited by the blowfly Lucilia cuprina fed human blood, semen and saliva

Adult flies of some species are known to be attracted to crime scenes where they feed on the proteinaceous decomposition products of dead bodies. The flies leave deposits through excretion and regurgitation, and these artifacts often appear morphologically similar to bloodstains. To date, little consideration has been given to the possibility of the fly artifacts containing forensically useful levels of human DNA, or of flies as vectors of human DNA. In the present study, groups of artifacts collected after the adult blowfly Lucilia cuprina fed on biological fluids were examined and found to contain human DNA sufficient for profiling. Random samples from each group of artifacts were then subjected to human DNA profiling. Of the samples analysed, full or partial human DNA profiles were found in 57% of samples deposited by flies after blood meals, 92% after semen meals, 46% after saliva meals, 93% after blood/semen meals, 58% after blood/saliva meals and 95% after semen/saliva meals. DNA from artifacts deposited after flies were fed blood, semen, saliva, blood/semen, blood/saliva or semen/saliva was extracted at various time points up to 750 days, and the human DNA component quantified. The human DNA extracted from blood- and semen-based fly artifacts demonstrated a clear trend in which the amount of DNA extracted increased over the first 400 days, and full human DNA profiles were still obtained 750 days after artifact deposition. Saliva- and blood/saliva-based samples were tested at intervals up to 60 days and generated partial profiles at this final time. Blood/semen- and semen/saliva-based samples generated full profiles at 250 days. The presence of human DNA in fly artifacts has considerable forensic significance. Fly artifacts could potentially compromise crime reconstruction, and/or contaminate DNA evidence, up to at least two years after their deposition. Alternatively, fly artifacts may be a useful source of DNA if an offender has attempted to clean up a crime scene.