BEHIND THE SCENES: forensic entomology

There is a suspicious death: human remains are discovered on the edge of a wood bordering a meadow. A municipal crew came across the corpse while collecting garbage. Police observed fly larvae (maggots) associated with the decomposing remains. The forensic identifier at the scene telephones me.

I arrive at the police command post and before anyone can comment, I say, “no thanks, I don’t want to know when you think he died, I need to remain objective in my findings”. Following the forensic identification people to the body, we move along the “path of contamination” which is the route police use to minimize chances of trampling evidence at the scene (this is the approach least likely to have been taken by the perpetrator). The body is an adult male lying face down, head through the bottom of rusted wire fencing and shrubbery.

“I need access to the head, that’s where blow flies usually first lay eggs” I say. The forensics snip wire and vegetation from around the head. I set to work sampling for insect larvae, taking the temperature of each collecting site first. I take samples of larvae and place them on bite-sized pieces of raw beef liver, effectively initiating rearing procedure. About one-half of the larvae will be reared to adult flies. I plunge several larvae from each sample into scalding water for a few minutes, then transfer the specimens into 80% ethanol. By killing some of the maggots I have effectively frozen the moment in time.

“This a bullet hole?” I inquire. Sure enough. The coroner has already been to the scene and pronounced the death, but forensics needed time to work the scene before body removal and autopsy — which I will also attend. Suddenly, there is a flurry of activity as they photograph anew the body. I stand aside, my own work temporarily placed on hold. Forensics reports to the command post. The suspicious death is now officially a homicide. Before leaving the crime scene in order to follow up sampling during the autopsy, I confirm that forensics have installed a temperature “datalogger” at the crime scene. The unit will continue to record crime scene temperature for the next week or so. Later, I will download this “climatological data” into my computer to compare crime scene temperatures to official Environment Canada records for the same times. The statistical comparison, and appropriate adjustments if necessary, will facilitate a retrospective capture of crime scene temperature data. In conjunction with known biological information about the species of blow flies recovered from the victim’s remains, I will be able to track back to the time when blow flies first colonized the corpse. Depending on environmental conditions, this time is often consistent with time of death. Such an insect investigation into decomposing remains will help the Coroner’s Office determine time of death when other scientific methods no longer apply.

Claim investigation

Hold it, this is an article about bugs on bodies and establishing time of death? What does this have to do with insurance? Consider the following example of an insurance claim where insects come into the picture — a case of insect infestation of foodstuffs (the names and places have been changed to protect parties). Using similar analytical techniques as above it was possible to determine the timing of an outbreak of Indian meal moth in a company work plant and, hence, the origin of insect infestation in a food product.

Snack-A-Rooney Inc. processes raw materials, including dried fruits nuts and grains into a health food treat marketed worldwide. Raw materials are received into the plant from several different suppliers, processed and packaged into product within a three to five day period, stored for up to three months, whereupon it is shipped to customers.

Disaster strikes

One fall day, Snack-A-Rooney’s CEO John Greeves is called by a Florida customer. The customer claims the snacks, wrapping intact, were being returned because “worms” could be seen through the transparent cellophane packaging. Snack-A-Rooney is suddenly flooded with calls and product returns. The company is further plagued by an outbreak of moths at its plant. Greeves alerts his insurance broker who sets in motion a claim. A claims adjuster is called in to investigate the claim, following which I was brought into the picture.

I visit the scene and take samples of the infested and still wrapped product as well as “clean samples”. I note that the returned product originated from the same lot number dating back three months, and then one and a half months earlier. I also discover that the company’s current moth outbreak is one of a series and get the quality control people to dig out the dates. During a tour of the facilities, I observe the adult moths stuck to the sticky traps are indeed Indian meal moths. “What kind of climate control do you have in here?” I inquire. Silence. The quality control people exchange worried glances. “Actually, there hasn’t been, it’s been turned off since spring. It’s pretty well the same as it is outside this time of year”, is the somewhat hesitant reply. They observe while I pencil in yet another item into my notebook.

Temperature data

Fortunately for Snack-A-Rooney there is an Environment Canada weather station close by. I expect the temperatures for both places to be comparable with minor variations in microclimate. I later procure the weather records through the claims adjuster. Could there be a direct relationship between the timing of the arrival of infested skids from suppliers into Snack-A-Rooney’s plant late spring and the subsequent moth outbreaks? Or, could the origin of infestation be explained through local means? The Indian meal moth is a common insect — could moths have flown into the plant from outdoors? Alternatively, could they have originated from within the plant itself? The possibility that a hefty amount of product had been simultaneously infested at retail outlets globally was eliminated after minute examination of the packaging. The packaging was intact and there were no means of entrance by adult or larval moths.

Insects and temperature

There are linear relationships between the development of most insects and temperature. There are also minimum temperatures below which development of the insect is suspended. The relationships vary between insect species, but this rule generally applies, and the Indian meal moth is no exception.

Literature research is now critical. Without specific information on the temperature dynamics of the Indian meal moth with respect to its developmental rate, any conclusions I may later draw will not suffer scrutiny by litigation experts, should push come to shove. Forensic entomology methodology is steeped in decades of research through the agricultural and forestry industries. I am not disappointed by what I find.

The amazing part of the methodology in this case is that relative humidity played a quantitative role in the analyses, whereas it does not in criminal cases using maggots. Fly larvae feeding on decomposing remains are almost totally immersed in a semi-fluid, then fluid medium. Humidity, therefore, does not matter to them. It matters to the eggs, in a qualitative sense, in that they need humidity in order to hatch and for young larvae to subsequently establish in their food substrate.

Indian meal moth larvae (caterpillars), colonize dried foodstuffs. The caterpillars are soft-bodied, with the exception of the head capsule, and naked. Relative humidity and moisture of their food substrate is therefore relevant to their survival and growth. Development at 22C degree, for instance, takes 24% longer at a relative humidity of 43% compared with a level of 70%.

Laying the cards down

My job as a forensic entomologist is to examine the pieces of the puzzle as simply and objectively as possible. This meant that Snack-A-Rooney Inc. had to lay all the cards on the table.

Little did they know when they reluctantly admitted to their series of moth outbreaks at the outset that it might work to their advantage. In fact, the best they were hoping for at that poi nt were guidelines to help prevent future occurrences. Nor could I have known at the time what the outcome would be. Until all of the pieces of the puzzle were established, I could not offer a complete picture. As it turned out, the moths could not have entered the plant from outdoors simply because temperatures had never sufficiently warmed up that spring, nor could they have originated from inside of the plant as “over-wintering moths” as Snack-A-Rooney did not hold raw materials that long. That left one other possibility, the moths were introduced through raw materials from one of the suppliers, and examination of the infested product under high magnification indicated what fraction of the product was being fed on by the moth larvae. If Snack-A-Rooney Inc. had not come forward when they did, the company and its insurer would not have received a claims settlement exceeding $250,000 — excluding further amounts due to business interruption coverage.cu