what is forensic entomology?
Adult Bluebottle fly (Calliphora vicina)
Source: National Library of Medicine
Forensic entomology is concerned with the application of zoological principles to issues of forensic importance, including the provision of assistance in the estimation of 'post mortem interval' - i.e. an estimation of how long the deceased has been dead for - based upon an evaluation of the type of insect present on the body or at the scene, and a sound understanding of succession patterns of insects in the environment in which the body was found.
forensic entomology (the Wellcome Collection)
forensic entomology in history
A local peasant from a Chinese village was found murdered, hacked to death by a hand sickle. The use of a sickle, a tool used by peasants to cut the rice at harvest time, suggested that another local peasant worker had committed the murder. The local magistrate began the investigation by calling all the local peasants who could be suspects into the village square. Each was to carry their hand sickles to the town square with them. Once assembled, the magistrate ordered the ten-or-so suspects to place their hand sickles on the ground in front of them and then step back a few yards. The afternoon sun was warm and as the villagers, suspects, and magistrates waited, bright shiny metallic green flies began to buzz around them in the village square. The shiny metallic colored flies then began to focus in on one of the hand sickles lying on the ground. Within just a few minutes many had landed on the hand sickle and were crawling over it with interest. None of the other hand sickles had attracted any of these pretty flies. The owner of the tool became very nervous, and it was only a few more moments before all those in the village knew who the murderer was. With head hung in shame and pleading for mercy, the magistrate led the murderer away. The witnesses of the murder were the brightly metallic colored flies known as the blow flies which had been attracted to the remaining bits of soft tissue, blood, bone and hair which had stuck to the hand sickle after the murder was committed. The knowledge of the village magistrate as to a specific insect group's behavior regarding their attraction to dead human tissue was the key to solving this violent act and justice was served in ancient China.
The washing away of wrongs. Sung Tz'u 1247 (from a translation by McKnight B)
blowfly larval development
Blowfly larvae (maggots) feed on cadavers, and forensic entomologists are able to utilise their skills to estimate post mortem interval by analysing the stage(s) of larvae present on the dead body, and determining how many days such a developmental stage larva would take to appear.
Larva development is temperature dependent, however, and environmental data needs to be available so that laboratory confirmation of development time for that species - at the temperature suggested by analysing weather/ temperature data for that geographical area in the preceding days/ weeks - can take place. An additional complicating factor in post mortem interval calculation is that large numbers of feeding maggots generate significant amounts of heat, and the 'maggot mass' effect must therefore be considered in any time of death estimation.
Blowfly life cycle
Source: National Library of Medicine, USA (Visible Proofs exhibition)
Blowfly (Calliphora vicina) development is a function of temperature
Thermal imaging of a feeding maggot mass on a piglet carcase (red denotes higher temperature than blue; piglet head on the left of the image)
forensic entomology field techniques video
Mathieu J.B. Orfila, M.D., and Octave Lesueur, M.D., Traité des exhumations juridiques… [Treatise on legal exhumations, and considerations on the physical transformations undergone by cadavers rotting in the earth, in water, in toilets and in manure]; Paris, 1831. 'Cadaver buried February 7, 1828, and exhumed April 24, 1828'. Chromolithograph, artist: Hippolyte Vanderburch. National Library of Medicine
Forensic entomology - an introduction