The maggot that knew too much
Investigating a murder scene is never pleasant. Investigators must handle bodies filled with maggots and beetles, but ever more often it is these that lead to the conviction of the killers.
Mervin Mansell, an entomologist with the Plant Protection Research Institute in Pretoria, is doing ground-breaking work unravelling insects' secrets at crime scenes. The forensic entomologist helps the South African Police Service solve crimes by studying corpses and the insects that feed off them.
"Forensic entomology can be used to determine the time of death, the site of death and even the cause of death," said Mansell.
"The first two things police do if they are confronted with a corpse is to identify the body and then determine a time of death.
When the police have a time they can relate to the murder, they can start looking for missing persons who were reported during that time frame. When they find suitable suspects they can ask relatives and friends when they last saw the person. If they have suspects they can check the alibi. These are all crucial facts in an investigation," he said.
Maggots help determine the time of death. "Insects invade the body in a series of waves that are characterised by one or more dominant species. There are approximately eight waves with complex ecological interactions," said Mansell. "We determine time of death by looking when the eggs were laid and how far the insects' cycles have developed."
The way a body is covered will determine which species of flies are attracted to it. They will lay eggs that develop into maggots. Weather conditions then play a role in the development of the maggots.
Each species has its own habitat preference. Some feed on exposed corpses, others only feed on old corpses. Most beetles, for example, arrive when the corpse is desiccated. One type of beetle feeds on bone. Another feeds on hair after it has been damaged by the wind and weather.
Investigators can even rely on insects to tell them how the victim died. Insects lay their eggs in the orifices of a body, such as the nose and mouth. Blowflies will concentrate on the facial region. If a body was mutilated before death, a heavy infestation might take place in body parts that are not affected when the victim is not mutilated. Blowflies are attracted to blood and will first head to the site of trauma. Investigators usually suspect sexual assault if blowflies have infested the genital areas.
Insects can even indicate if a body has been moved.
Inspector Vivian Bieldt of the police forensic laboratory in Silverton, Pretoria, said that Mansell's work is irreplaceable. He remembers working on a case with Mansell where a suspect was caught out in a lie with the help of entomological evidence.
"We discovered a body that had been covered with plastic and sand. The insects couldn't get at the body, but Mervin discovered that the body had dead maggots underneath the clothes. This meant that the body was exposed prior to being covered. The body had to have been covered and moved, which suffocated and squashed the maggots in the process. When confronted with this evidence, the killer realised that he had no way out and confessed to the crime," said Bieldt.
Drugs and poisons also show up in maggots that feed off flesh. Analysing the maggots can show if the victim had been drugged or had been drinking. Heavy metals and some drugs stay in the insects months after the victim's death.
Collecting insects from dead victims can be gruesome, but Mansell tries to avoid learning about the victim as a person. "I make a point of never finding out who the victim is. The cases are so harrowing that you have to distance yourself and treat the case as cold hard evidence. It may seem cold, but to allow yourself to get involved personally would only damage you in the long run."