Entomology insects know where they are going

This is how insects help solve murders

In order to identify murderers, criminologists try to clarify the time and circumstances of an act as precisely as possible. Living traces of all things provide them with particularly valuable clues: insects

On the evening of June 9, 1959, 14-year-old student Steven Truscott cycled through the town of Clinton in the Canadian province of Ontario. His twelve-year-old schoolmate Lynne Harper sat on the handlebars. It was the last time witnesses saw the girl alive.

Two days later, Lynne was found strangled on a dirt road near the town. When police interrogated him, Truscott said he dropped the girl on the road where she got into a Chevrolet. However, because he became embroiled in contradictions, the teenager was charged with murder and sentenced to death.

Given his youth, the sentence was commuted to life imprisonment. Truscott himself always protested his innocence. The case attracted a lot of attention and contributed significantly to the abolition of the death penalty in Canada. In 1969 the young man was pardoned, but lived on with the stigma of being a convicted murderer.

It was not until 48 years after Lynne Harper's death that he was declared "not guilty". Truscott owes his rehabilitation to a few tiny, white larvae that coroners found on Lynne's dead body and documented precisely: maggots from a blowfly.

These often very pretty, metallic shimmering insects occur in more than 1000 species worldwide. While the adult flies feed on pollen and nectar, sugary foods and various excretions, their larvae need protein-rich food. They find blowflies in the dead body tissue of other living beings. They are among the most important organisms that decompose carrion in nature and thus return dead bodies to the earth's material cycle

The maggots grow with the precision of clockwork

Blowflies have such a good sense of smell that they can detect the earliest decomposition processes in a dead body. Therefore, they are usually the first insects to colonize fresh carcasses. If the weather is favorable, the animals can lay their eggs on a corpse just minutes after death.

Depending on the temperature and humidity, larvae grow out of these eggs with clockwork precision, known in flies as maggots. Each species follows its own characteristic development cycle. The maggot of the blue blowfly hatches at a temperature of 27 degrees Celsius 24 hours after the egg is laid. The next day it measures six millimeters, after another day 13 millimeters in length. It pupates again two to three days later, and hatches as a finished fly around four weeks after the egg is laid. Then the cycle begins again.

Insect insightful

Less than an hour

Blowflies are the first insects to seek out a corpse. Their sense of smell is so precise that minutes after death they smell decomposition processes and lay eggs on the corpse.

At least a day

Depending on the weather, maggots hatch from the eggs after a day and feed on the dead meat. Each species has a typical development cycle.

Two to three days

Short-winged beetles appear after two to three days. They feed on the decaying tissue and primarily target the insects that are already there.

A few weeks

Blowflies dominate the first few days of decay, initially few other species are found. If forensic scientists detect swinging flies, the corpse has been decaying for a long time.

Some months

Because of their mouthparts, bacon beetles are able to eat away skin and cartilage remains - and they attack a corpse very late.

The length of the maggots relieves Steven Truscott

When forensic scientists re-examined the evidence in the Harper case in 2007, they found that the maggots found on the girl's body did not match the assumed time of death: if Lynne had really died on the evening of June 9th when she was seen with Truscott , the white larvae should have been a few millimeters longer. The experts concluded that the child was only murdered on the morning of June 10th. Steven Truscott was no longer an option. He later received $ 6.5 million in compensation.

Truscott was unlucky that insects as clues were not yet common in court in the 1950s. It was not until the 1970s that “forensic entomology”, that is, forensic and criminal entomology, developed into a recognized discipline.

According to tradition, a murderer was unmasked with the help of insects as early as the 13th century: residents of a Chinese village had found a dead man who had been killed with several blows of a sickle. Then the legal scholar Sòng Cí had all the farmers in the area line up with their harvest knives. After a short wait, flies settled on a man's blade - traces of blood invisible to the naked eye attracted them. Convicted in this way, the perpetrator collapsed and confessed to the murder.

Humpback flies even dig up to buried corpses

And as early as the 19th century, European scientists carefully studied the insect fauna on corpses and documented the species discovered. Today there are even so-called “body farms” in the USA, where researchers decompose dead bodies in order to examine the decay process and the insect colonization of the corpses under changing environmental conditions.

Because blowflies are the first, but by no means the only boarders to feast on carrion. A dead body, whether an animal carcass or a human murder victim, is a veritable ecosystem that changes over time and provides food and habitat for dozens of species.

Shortly after the blowflies, house and meat flies appear, later the humpback flies. Representatives of this group are particularly informative because they can dig and thus also get to buried corpses.

In later stages of putrefaction, cheese flies as well as carrion and dung beetles appear, including the common gravedigger, a conspicuously black and orange patterned animal. When the carcass gradually dries up after weeks and the blowflies start looking for fresher food, it is time for the bacon beetles. They prefer leathery, tough organic material and are notorious as museum pests, as they also like to nibble on ancient mummies and animal preparations.

After a certain time, all these species are joined by predatory insects, which are less interested in the rotting meat than in the scavengers themselves. Ants collect fly eggs, while nimble rye beetles, often only a few millimeters in size, hunt maggots in their carcasses.

This typical sequence of insects, which occur on corpses in different stages of decay, makes it possible to determine how long the body has been decaying. Entomological dating is often amazingly accurate even after a long time, when a doctor has long since had to agree. The determination of the time of death is thus the most important area of ​​application of forensic entomology.

Maggots also tell where the victim died

But the teeming life on a dead person can provide further clues: The maggot species can be used, for example, to determine whether a murder victim was moved to another location after the crime. If the coroner finds housefly larvae on a corpse that was lying in the forest, he can assume that the victim did not die there, but in a house. Because houseflies usually live in buildings or their surroundings.

Some types of fly, such as the blue blowfly Calliphora vicina, are city dwellers, while the closely related species Calliphora vomitoria mostly found in the countryside. Some flies frolic in the sunshine, others love the shade. The colonization of a corpse allows conclusions to be drawn about the type of environment in which it spent the first hours after death.

For this reason - and because the development times of even closely related species differ - forensic scientists have to determine their insect finds unequivocally. It's not exactly easy with fly maggots, as they are pretty minimalist, worm-like creatures. Experts can determine the genus based on a few bristles or body tags. In order to determine the exact species, however, one had to collect and raise living maggots a few years ago.

Today, genetic analyzes, which have become faster and cheaper in recent years, simplify the work of forensic scientists. The gene sequences of the most important corpse residents are available in databases.

The insect forensic scientists have an enemy: the cold

Investigators are also increasingly interested in the insects' stomach contents. Because with the body tissue of the dead, the animals also ingest drugs or poisons that the victim may have ingested shortly before death. Since maggots cannot break down such pollutants, they accumulate in their bodies and are stored in the shell when they pupate. Forensic doctors can still detect traces of poison in empty doll covers after a long time, when no more samples can be obtained from the dead person.

Insects can even reveal something about murder victims whose bodies are never found: For example, if investigators discover maggots in the trunk of a suspect, they can isolate the deceased's DNA from the animals' digestive tract and identify him based on his genetic make-up. This would prove that the missing person was in the car - and that he was already dead.

Forensic entomology is able to solve murder cases in which the conventional methods of criminalistics fail. However, it has one weakness that even the most modern molecular biological methods cannot make up for: it is and will mainly be a seasonal business. If the temperatures drop, blowflies and beetles will stop reproducing at some point above a certain, species-specific threshold value.

In severe winters, no insect disturbs the peace of the dead.