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An Insect-or Calls

27 Jan

A blood curdling scream disturbs what was otherwise a calm summer’s eve, and then all was deathly silent again. The butler comes running into the reading room looking distressed,

“It’s the gardener ma’am, she’s found something in the rose bushes. It’s a young man. It’s the body of a young man!”

“Not to worry”, a voice pipes up from the corner of the room, “I’m an entomologist”. The others look at each other bemused, “The name’s Crawley, Dr Carrie P. Crawley”.

The corpse bride

Forensic entomology uses details known about the lifecycles of necrophagous (corpse-eating) insects and arthropods to provide valuable information regarding “time of death”. It’s true, I saw it on CSI. But don’t take their word for it, Professor Saloña Bordas, a visitor to Reading University from the Universidad del Pais Vasco, does this kind of thing for a living. A short while ago I went to see her talk, intrigued by the idea of forensic entomology. After listening for about ten minutes I thought – she was mad – a large part of her research involves leaving dead pigs to decompose under different conditions in order to understand how environmental factors such as geography, climate, altitude and habitats might alter the lifecycles of these crawly flesh fanciers. After an hour of images that made me want to scrub my eye sockets clean, I found myself still morbidly fascinated by the process.

Historically, this form of crime investigation dates back to the 14th century with a Chinese judicial intendant, who wrote a detailed handbook for coroners. In it, he describes a particular case study from a small Chinese village where a victim is found stabbed to death in a field. After testing multiple blades on animal carcasses, it is concluded that the murder weapon was a sickle. All the villagers were asked to bring their sickles and lay them out in front of the crowd. Suddenly, blow flies began to gather on one blade, which, he deduced, must have had remnants of blood and tissue, no longer visible to the human eye. The man broke down and confessed to the crime, and was sentenced accordingly. Here however, things go quiet, and it is possibly because it took a further 300 years to make the connection between maggots wriggling in a carcass and flies landing on the scene of a crime. It was originally thought that maggots developed spontaneously from rotting flesh, until in 1668, an Italian physician showed that meat needed to be exposed to the air in order to become infested with maggots. At this point people began to understand the complex and fascinating lives of insects and arthropods which go through multiple moults through their life in order to reach their adult form. Entomology developed as a science, and finally, in 1881 Hermann Reinhard, a German medical doctor, showed that different insect species could be biologically dependent on finding carcasses in order to complete their lifecycle; and so the field of forensic entomology was born.

Despite its long history, it is only within the last 30 years that is has begun to be used in murder investigations, and it is still not widely practised. Unfortunately, this means that many crime scene technicians, homicide investigators, coroners, medical examiners, and others involved in the death investigation process, are not familiar with the techniques of the trade – leading to a lack of standards between cases and disputable validity as evidence in court. However, under certain stable conditions the lifecycle of key necrophagous species becomes very predictable; you just have to know what to look for. The most important things to note are which insect eggs are present, what instar (growth phase) any larvae might be at, where any eggs and larvae are present within the corpse, and in what order they appear. Once you have this information you can begin to piece together the puzzle, and hopefully considerably narrow the window in which death could have occurred.

So let us go back to our crime scene in the rose bushes, how would Dr Carrie P. Crawley begin her investigations? Firstly, she would need to look for signs of infestation by necrophagous species. A big heaving mass of maggots confirms that the body is infested. Next, using her keen knowledge of fly biology she identifies the maggots as blow fly larvae in their second instar. The blow fly are the most likely species to reach the carcass first thanks to a super sense of smell, which can detect the smell of flesh from up to 10 miles away. When they arrive they lay eggs immediately, and these will begin to hatch into maggots within about 24 hours, moulting and reaching the second instar after about another 27 hours, so the body is likely to be between 48 and 72 hours old. In order to get a better estimation time since infestation she takes the air temperature, and then – the grim bit – Dr Crawley would place a thermometer into the writhing body of maggots and record the temperature at the larval mass core. Next the ground temperature is taken, as well as the temperature at the interface between the body and the ground. You may have detected a theme here; temperature is a vital cue for the lifecycle process, and the more accurate the readings and the more stable the environment, the more precise the estimation of time since death can be. This was crucial in a recent case in Illinois (http://www.carmitimes.com/newsnow/x638337376/Murder-trial-begins-in-Harrisburg); the body of the victim was discovered inside, and as such investigators were able to provide an entomologist with the exact temperature at which the body stayed during decomposition. After identification of the samples sent from the scene, the time of death was decisively narrowed down to have occurred within a two day period. This evidence turned out to be key to the trial, because the defendant claimed to have spoken to the victim during a time at which the entomological forensic evidence shows the victim was dead.  But, back to our murder case; next she would need to take into consideration weather data that included the maximum and minimum daily temperature and rainfall for a period spanning 1-2 weeks before the victim’s disappearance to 3-5 days after the body was discovered. In this case we know it was a summer’s evening, and we know the body was discovered in a well-tended garden, suggesting that the ground would be well watered – so we can assume the conditions would be ideal for the flesh feasting beasts and processes of decay to be happening very fast. Next specimens of the species present would need to be collected, from the body, and from the areas surrounding the body, to check for larvae which might be feasting on bodily fluids which could have leached into the soil (I do hope you’re not trying to eat while reading this). After all this, the species need to be identified and all the data combined in order to gain the most accurate estimation of time of death.

And so, after all this painstakingly meticulous work, what did she conclude?

The butler did it… figures.

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