Diptera in the Forensic Investigation of Human Deaths in Great Britain and the Dominant Role of Calliphora vicina (Calliphoridae) in Estimating a Minimum Post-Mortem Interval

Saprophagic flies can have a vital role in forensic investigations of suspicious death by providing an estimate of the minimum post-mortem interval (minPMI). An exemplar blow fly species, Calliphora vicina (Diptera: Calliphoridae), is frequently reported as being of greatest importance in this role, but without significant corroborating evidence. Therefore, the present study examined 122 anonymised, historic cases of suspicious death investigated in Great Britain (GB) to determine the role of Diptera and of C. vicina in particular. Thirty-seven fly species in eighteen families were recorded, with greater diversity outdoors (17 families) than indoors (11 families). Family diversity and the age of the oldest developmental stage increased as estimated minPMI increased. Indoor minPMIs tended to be lower than outdoor minPMIs, probably due to the higher likelihood of finding a body indoors. The most commonly collected family and species were Calliphoridae and C. vicina, respectively, the latter recorded in 69.7% (85/122) of all cases. The four main reasons for the importance of C. vicina are: (1) widespread distribution; (2) broad seasonality; (3) low thermal tolerance; and (4) ability to colonise bodies soon after death. It was used to determine minPMI in 85.9% of cases in which it was collected (73/85). Where a most likely PMI could be compared by regression analysis with a minPMI from C. vicina evidence, the relationship was robust (R2 > 0.98), accurate to within 2.5–2.7 days at a most likely PMI of 20 days. With greater research effort, Calliphora vicina and more neglected fly species can have an increasing role in future forensic investigations of suspicious death.