Close up of Golden Hill's brown blowfly (Diptera: Calliphoridae: Calliphora hilli)

Entomology has had a profound impact on growing thousands of death investigations. The infestation of blowflies and other fauna on decomposing remains can provide vital clues to a manner and cause of death, depending on the environmental conditions.

An Australian team reports now that the human DNA samples pulled from blowfly feces is an overlooked source of forensic clues at some crime scenes, they write in the Journal of Forensic Sciences today.

Such DNA sources can yield genetic profiles for two years – or more, according to their work.

“The present findings highlight the need for crime scene examiners to be aware of the presence of potentially human DNA-bearing blowfly artifacts in all areas of a crime scene, not just warm or well-lit areas,” the researchers write. “If a crime scene has been cleaned by the offender in the immediate vicinity of the offense, examiners should be aware they may find artifacts, and consequently potential sources of human DNA, in a number of locations around the scene.”

Four mock crime scenes were set up in a vacant house, without furnishings or climate control – but with virtually every surface covered by Kraft butcher’s paper.

The experiments moved a sample of human blood (about 150 mL) around the various rooms of the house, followed by the release of hundreds of blowflies in different parts of the dwelling. The location of the flies, the feces and regurgitated material were all catalogued after 72 hours.

The blowfly that was being investigated was the Lucilia cuprina, otherwise known as the Australian sheep blowfly. (This is different than in North America. The flies of most investigative use in the Western hemisphere are the common housefly Musca domestica, the bluebottle Calliphora erythrocephala, the greenbottle Lucilia Caesar, and the sheep maggot fly called Lucilia sericata, according to the textbook Practical Homicide Investigation by Vernon Geberth).

The traditional belief is that these opportunistic feeders move toward food and toward light during key phases of their lives – and that most of their traces will be found in ceilings or high on walls.

But the four crime scenes in the vacant house showed that, while that is generally true, the circumstances changed the locations of the traces significantly enough to cause reconsideration of many crime scenes.

“The results dispel the commonly held view that artifacts are predominantly found in high and/or warm areas,” they conclude. “It was found that flies may move toward warm or well-lit areas and deposit artifacts there, but artifacts were predominantly located around food sources and were often found in low positions.”

Ambient temperature, changing light and the moving food source, caused different locations of the artifacts, the researchers add.

Stains that appear nowhere near traditionally defined points of interest may thus be a rich source of evidence, they write.

“Knowledge of blowfly behavior in this context will also ensure crime scene personnel are aware of the variable distribution of artifacts so an ambiguous spot is not dismissed as unlikely to be a fly artifact due to its location in an ‘unexpected area',” they add.

Three of the four authors of the current study also authored a paper in 2013 in the journal Forensic Science International that found that human DNA profiles could be found in 57 percent of the flies’ feasts on corpse blood – and as high as 95 percent in meals that also included semen. The DNA profiles were still obtained more than two years after the flies deposited feces at the experimental scenes, they added. The DNA source could either contaminate a scene with misleading genetic information – or help crack a case, the researchers concluded four years ago.

“Fly artifacts may be a useful source of DNA if an offender has attempted to clean up a crime scene,” they said.