Maggots and Beetles and Flies, Oh My! How Forensic Entomology Solved the Case of a Burning Body

Episode Transcript

The year is 1997. Police are called to a house fire in Perth, and once the flames are out they find the body of a man inside. He had been murdered before the fire was lit, but neighbours said they had not seen anyone coming or going from the house on the day of the fire. Police are at a dead end. Then a blood soaked doona is found in a bin near the house. Some big, juicy maggots are found on it… and they change the course of the investigation.

In this episode of CS-Science we’ll look at how maggots, and other insects, can be used to solve crimes, and how they were used to solve THIS crime… as we take a look at Forensic Entomology.

The first known forensic entomologist was Song Ci. He published a book in China in 1247 called ‘The Washing Away of Wrongs’, basically the world’s first forensic science textbook! In it he describes the murder of a villager who was stabbed to death. Authorities identified the culprit by having all the peasant workers lay out their sickles. Flies were attracted to one sickle, the one that had invisible amounts of blood on it, and its owner was arrested for the murder.

But in most forensic entomology cases, the insects are found not on the murder weapon, but on the body.

Well maggots actually DO ‘stand up in court’ and give evidence. Well, they don’t actually stand up in courst, but that would be cool.

But maggots and other insects do provide evidence to investigations, particularly to work out how much time has passed since someone died.

Insects are useful because they have life cycles with very distinct stages.

A mumma fly comes along and lays her eggs. These eggs hatch into maggots, also known as larva. The maggots feed and grow, and eventually have to shed their skins in order to keep growing.

They do this multiple times, and each stage of growth is called an ‘instar’.

After reaching their final instar they pupate, that is they form a hard shell around themselves while they metamorphose, and eventually they emerge from the pupa as flies, ready to start the cycle again!

Each of these life stages takes a known amount of time (although there are some complications which we’ll talk about a bit later).

So, for example, if a body is found with cute little instar 1 maggots it can be estimated that the body has been there between 23 and 27 hours.

But if pupae are found on the body, it must have been dead at least 130 hours, or 5 days!

So back to the body in the burning house. The forensic entomologist could tell that the maggots found on the bloody doona were 3 days old, indicating the murder had taken place DAYS before the fire. When they reinterviewed the neighbours, they found out that the murdered man had been heard arguing with his brother 3 days before. It turned out his brother had killed him during the argument, and then returned to the house 3 days later to destroy the evidence by burning it down.

But, it’s not always that simple. The arrival and growth of flies and maggots can be affected by a range of environmental factors, such as the temperature, the season, whether the body is in the shade or the sun, if it has been raining just to name a few.

It also makes a difference whether the body has been buried, covered, or left out in the open. And if a body has been kept sealed away from insects altogether maggots cannot grow, no matter how old the body is.

And of course, different places have different species of insects, so it is important to have local knowledge. Until as recently as 2016(!) all the information about what happens to human bodies  left outside after death came from body farms in the US. But that has now changed…

It’s also important to remember that it is not just ONE species of fly that will visit a body. There are entire ecosystems that pop up around bodies, and each species has its own arrival times and life cycles. Here are some of my favourites.

The well named Flesh Fly, who is kinda cool because she lays live young instead of eggs.

This little guy called the Cheese Fly, because he’ll only visit a body when it has decomposed enough to smell like cheese.

And the Carcass Beetle who prefers the body when it is more like beef jerky, and only comes to feed once it is properly matured.

And then we have the parasitic wasps, that don’t come to feed on the body at all, but to lay their eggs inside the pupae of the flies that are feeding on the body.

And once all the flies have finished up and moved on, along come the moths to feed on the hair.

So there’s a lot going on!! A body becomes its own little ecosystem!!

If it wasn’t already complicated enough, forensic entomology is also being influenced by climate change.

The Common Green Bottle Fly is used by forensic entomologists in the US state of Indiana (and many other places) to work out time since death.

But as temperatures have risen, some fly species have migrated to cooler climates.

The Australian Sheep Blowfly which only used to be found further south, has migrated and is now also found in Indiana.

Why does it matter? These flies look VERY similar, even to entomologists! But they arrive at a body at different times, so mistaking one fly for the other will cause scientists to arrive at the wrong time of death. Thanks global warming!

So that’s been just a little insight into the amazing world of forensic entomology. A world where the closer you look, the more you see. I’ll leave you now with just one more close-up look at this wonderful world, a photo of a beetle’s head.

So cool… So that’s all from CS-ScIence, remember to Like us on Facebook, Follow us on Instagram and Twitter, and check out our new webpage. – catch you around!