The policeman's fly
Audio 02:39
Flies also like to forage on flowers.
© Getty Images - MICHAEL CORCORAN
By: Florent Guignard Follow
3 mins
Scavenger Diptera, more often known as poop flies, are allies in criminal investigations.
Report at the Criminal Research Institute of the National Gendarmerie, near Paris, where flies recovered from corpses are used to date the death of a victim.
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They are sticky, sometimes noisy, and you find them repulsive, so much so that you call them shit flies. But some gendarmes make allies of them. This is the case at the Criminal Research Institute of the National Gendarmerie (IRCGN), in Cergy, near Paris, and more specifically at the FFF department, for forensic fauna and flora, scientific techniques in the service of justice: how plants or animals can help investigators solve crimes.
For example, there is forensic palynology, the study of pollen grains found in the respiratory tract of a corpse, to date the death of a victim, since plants only release pollen at a certain time.
And so there is also forensic entomology, when insects, necrophagous Diptera, also shed light on the work of investigators.
Sacred voracious, these necrophagous diptera, which thus feed on corpses.
"
We had taken a 25-kilo pig, in the forest of Fontainebleau, south of Paris, and from memory, in 13 days, the carcass was completely cleaned
", says Captain Hubert Joulin, the head of the FFF department of the Institute. of criminal investigation of the national gendarmerie.
In wounds or natural orifices
These detritivorous insects, in a criminal investigation, will be taken from a corpse and from the crime scene, in particular the larvae they have laid in the rotting flesh. “
Some species are attracted to the body upon death, if there are wounds or even to natural orifices. All this fauna will develop and the important thing for us is to have a sample that is as representative as possible of the crime scene, in the hope of finding the oldest individual.
This will make it possible to go back in time, and to approach as closely as possible the date of the presence of the corpse.
The seals, which contain larvae and earth taken from around the corpse, arrive at the IRCGN in Cergy, where the identification of the species taken can begin, in austere premises, blind rooms without daylight – we are far from the tinsel of the standard American series
The Experts
… “
The living species will be put in breeding, in incubators.
» Species of large fridges, where the temperature is regulated and controlled, and where trays are stored
.
Breeding on a Steak
“
You can see a bed of sand, beef. No, we must not believe that it came from the body of a victim, we only have insects that come to us! On the piece of meat, you can see larvae coming and going”
, describes Hubert Joulin again. It is this meat that the larvae feed on to grow
.
“
After a while, they will form a pupa, the equivalent of the chrysalis of butterflies for Diptera. And after a while, an adult will come out.
»
This will make it possible to identify the species found on the corpse, and therefore, depending on the temperature readings and the environment of the crime scene, to precisely date the day of the laying, to say: the corpse was already there on such date.
And very often, the investigators hit the mark.
"Do shitflies really like that?"
Ah yes, they like corpses, excrement, all the decomposing matter, because they are rich in nutrients.
To feed on it, the fly leaves a little saliva on the poop, before sucking it all up.
Adult flies also lay their eggs there, warm and well fed, the pantry at home.
It's a bit like Lavoisier's law adapted to scatophagy or necrophagy: nothing is lost, everything is transformed.
And they even do the cleaning!
Don't worry, these flies don't just have a life of excrement: they also like to forage on flowers.
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