There are some crime-scene witnesses one simply cannot grill.

They buzz about or linger, altering the landscape, and there is nothing one can do to stop them. But take a closer look at their work and one realises that the insect invaders are some of the sneakiest and stealthiest detectives of them all.

It doesn’t matter if a body is hidden in a bog, in a suitcase, underground or underwater, they will turn up. From the minute they do, they start to tell a tale.

The first thing they reveal is timeline. How long has the person actually been dead?

Within minutes, above ground, the blowflies tend to arrive. Weeks in, the beetles and mites turn up. If there are skipper flies around, that means the body has likely been in situ for months.

The presence or absence of insects can prove that a body has been shifted. How else would a blowfly from Shimla end up on a body found in Kerala? Insects can point to foul play and cause of death, as when a chemical analysis of specimens and larvae reveals traces of poisons or drugs.

There have been cases in which an insect destroyed an alibi. And cases in which, because of them, a “heart attack” was proven to be murder. (Turn to the case studies alongside for more on this.)

Of course, in order for any of this to hold up in court, an expert must be able to vouch for each detail: species, region, proof of time elapsed. And so, around the world, small groups of forensic entomologists are studying insects, analysing crimes, and helping law enforcement draw credible links between the two, in a field that has been evolving rapidly since the 1990s, alongside the boom in molecular biology.

It might seem from all this that most forensic entomologists cannot sit down to a cup of tea without being called upon to crack a case wide open. Sadly, this is not true.

There simply aren’t enough police departments that even know they’re out there.

“Because awareness about this field is still missing among law enforcement agencies of various countries, we are often not even consulted,” says Paola Magni, who has been helping crack cases and reveal gruesome details for over two decades, and is also an associate professor at Murdoch University, Perth.

“Many of the cases I’ve consulted on in the past two decades have come to me months or years later,” she adds. “In some of these cold cases, or when the cases are very old, one has to work with scarce photographic evidence of the bugs seen at the scene of the crime.”

It might help if there were more of these experts flooding the field, encouraging wider adoption of this science; but a lack of demand keeps numbers low, and so it goes, until, presumably, the gradual cycle of change alters the formula, as it did with forensic psychiatrists.

Meanwhile, another significant challenge is baseline data.

In this strand of forensic science, every detail is heavily defined by factors such as environment, temperature, humidity, location. These factors alter the decomposition process and the arrival and life cycle of the insects. And, there are tens of thousands of species to be studied, in a single state alone.

This is why a big part of forensic entomology today is collecting baseline data for different regions, climatic zones and species, says Devinder Singh, pro-vice chancellor and professor at Chandigarh University and one of India’s most renowned experts in this field.

Researchers are, for now, focusing on the most common insect families involved.

At Arizona State University, Jonathan Parrott, a forensic entomologist and assistant professor, has been developing a genetic and developmental database on blowflies. He and his students are working with thousands of the insects at any given point, compiling morphological and genomic data across species, for Arizona and surrounding states.

In India, a lab in Haryana has been using cadavers of pigs and rabbits to study different insects, their life cycles and their role in the decomposition process. Led by Sapna Sharma, associate professor at Maharshi Dayanand University, Rohtak, one of their recent projects focused on drowned bodies. A total of 2,385 insect specimens were studied during the city’s different seasons.

“At the local government hospital attached to the medical school, a lot of drowned bodies from the city’s many canals are coming in for post-mortem,” Sharma says. “We hope the study will help with cases of drowning victims.”

In addition to cases of death and murder, there are other areas in which the word of forensic entomologists is proving crucial, such as urban forensic entomology and stored-product forensic entomology.

In the first, one might seek to answer questions such as: What is causing a home, hotel or public building to be infested, and who is to blame?

In the second: How did that worm get into that sandwich and how long had it been there?

Back to crime scenes, Sharma and Singh are among those trying to get police departments to collaborate more closely with experts from their field. The first thing they would like to do, says Singh, is get the police to stop sanitising crime scenes. “Valuable insect information is lost in this way.”

He and others in India have offered to conduct training sessions for police personnel, “but the response hasn’t been favourable,” he adds. The reason, Sharma guesses, is that the idea is simply too icky, even for a policeman. “Working with a dead body is undesirable enough. Handling insects to boot… most people revolt at the idea,” she says.

This hesitation is one of the reasons Magni launched her SmartInsects app in 2013. It aims to help crime scene technicians understand the importance of insect evidence. It offers guidelines on how to collect and store samples. And it offers a reminder that they must also record environmental data such as temperature and humidity.

All those pieces need to fit together if insect evidence is to count. But when they do, “insects really are tiny witnesses. They can help us get justice,” Magni says.

.

Justice league: Real-life cases that insects helped crack

“It can be a huge responsibility, knowing that one’s work could change the course of several lives,” says forensic entomologist Paola Magni.

She has practised in Italy and Australia for over 20 years. Some of her cases still haunt her: What if she had never been called in; what if the true story of the victim’s final moments had never been revealed?

How telling can such evidence be? Take a look.

A heart attack turns out to be murder

A teenage girl was found dead by a lake near Rome, in 2012.

Federica Mangiapelo, 16, had a dislocated shoulder, a missing handbag and no cellphone. But the police could find no evidence of foul play. She seemed to have suffered an epileptic attack and then cardiac arrest.

Her family didn’t buy it. They suspected that her boyfriend, Marco Di Muro, 23, was involved.

He told police he had never been to the lake. Yes, he and Federica had fought the previous night. He said he then dropped her off on a street near the lake and drove home; there was no evidence to say otherwise.

That’s when Magni stepped in. A police officer remembered a presentation she had made at a training academy, on aquatic forensics, and contacted her. In her sessions, Magni had mentioned that when a crime occurs in a body of water, plankton can offer clues to what really happened.

In this case, what they needed was to confirm the boyfriend’s version of events.

Let’s test his clothes, Magni told the police. His clothes had never been examined. It turned out, some of the tiny, persistent plankton species had clung to his garments, and they matched the plankton species found at the lake.

This finding caused the case to be reopened, and a second post-mortem confirmed that the same plankton was present in the tissues of the victim, confirming a death by drowning. 

Di Muro was charged, and convicted in 2015. He is currently serving a 14-year sentence.

A mystery unravelled

When the highly decomposed body of a woman was found wrapped in layers of plastic, quilt and carpet, days after her death, the Turin police called on Magni. Could she help build a timeline of the case?

Studying the large number of insects now present on the body, Magni was able to approximate the time of death at 12 to 14 days before the crime was uncovered.

The victim was a commercial sex worker, and the police’s prime suspect had been her agent. But given the new timeline, he would have still been in prison at the time, serving a sentence of some weeks. They shifted focus to another agent she had been working with, but it turned out he had been out of the country on the dates in question.

The investigators began to look more closely at other clues, and returned to phone conversations and text messages that the woman had exchanged with another man, around the time of the murder. Interrogated by the police, he confessed. He loved her but she did not reciprocate his feelings, and so he killed her, he said. He is currently serving a 30-year sentence in the case.

A mummy tells a lonely tale

One of the most complex cases Magni has worked on involved a man found in his home, so long after his death, that his corpse had dried out and become almost mummified.

Even she couldn’t tell when the insects present had begun their work. Different species seemed to provide conflicting information. She had never seen anything like it, she says.

The police had only stumbled upon the man when they visited his home to investigate a series of unpaid fines.

But, as she studied this unusually advanced state of decomposition, Magni noticed something unusual: thread-like structures across the body, produced by larder beetles, usually found only months after a death has occurred.

Given that insects typically arrive at such a scene in what are called successional waves, one species always following another in a set pattern, Magni was able to finally unravel the clues. From the remains of blowflies that had fed on the body, the larder beetles in the body and in the upholstery of the couch where he was found, and the spiders that had arrived to prey on these and other insects, she was able to estimate that the man had died about 18 months earlier, of natural causes. Sadly, no one had even known he was gone.