Insects: first at the scene

Police are almost never the first at the scene of a murder: blow flies can arrive in just 15 seconds.
03 May 2016

Interview with 

Dr Martin Hall, Natural History Museum, London


If there's been a murder, it's not often the police that are first one the scene. MaggotsThere's something else which can arrive in as quickly as 15 seconds. Insects, which collect around bodies can provide vital clues, which is why entomologists, scientists who study insects, like Dr Martin Hall are often called in to help with forensic investigations. Georgia Mills visited Martin, at the Natural History Museum in London, to find out about one of the oldest forensic sciences...

Martin - Forensic entomology has got quite a long history.  There are even reports from 13th century China about insects being used to help solve crimes but really things started to get underway in the UK in 1935 when there was a famous case of Buck Ruxton who murdered his wife and his wife's maid, dismembered their bodies and threw them into a ravine, and when the body parts were found, many of them contained magots. And we've actually got in our museum collection some of the magots here.  They don't look very impressive - small brown things - they obviously weren't preserved very well.

Georgia - These are the magots from the actual case?

Martin - Yes, that's right,  yes - these are the actual ones, so from 1935.  They were identified as a blue bottle fly and have the lovely name Calliphora vicina. It's actually the most common Blue bottle on bodies in the UK. So back in 1935, the scientists aged these maggots and that aging fitted in with a witness who was knocked off his bicycle. He managed to write down the number plate of this car and it happened to be Buck Ruxton's car. It was him basically making a quick getaway from the scene where he dumped the body parts and it helped steer the investigation in the right timeline.  But it was the first time that magot evidence was used in the investigation. He was actually found guilty, Buck Ruxton, and hanged for those murders the next year in 1936 in Strangeways Prison, Manchester.

Georgia - It's incredible to look at these tiny shrivelled things in this jar. It's amazing to think they actually had an impact in a forensic investigation.

Martin - Absolutely, yes. Blow fly adults, they respond to the odours of decomposition amazingly finely and they have antennae on the head which act like the nose basically.  And I've got a sheet of sticky paper over here, you can see when I pull back the top here...

Georgia - Oh - it's full of flies...

Martin - It's covered in flies.  These are mostly Green bottle flies, actually. These were caught in Hungary and this sticky sheet was just place over a rat in an experiment and all of these flies have come in to land on this dead rat.

Georgia - There are hundreds...

Martin - Yes, exactly.  So they can detect the odours of decomposition really early and they'll arrive very soon after death. In our experimental works here in the museum, we use pig heads because they're cheap and easy to come by and sometimes, when we unwrap them up in the tower which is eight floors up, we'll have Blowflies arriving within 15 - 30 seconds.

Gerogia - Not only was I treated to a sticky tape full of flies, but Martin also had prepared a glass box of, very much alive, maggots, some of them had already started developing hard cases as pupae, but most of them were squirming along very unpleasantly.

Martin - So these maggots we've got in front of us are squirming around yes, but doing it rather lazily to be quite honest because it's a bit cold in this cocoon in the museum here. And what I've done is I've just taken out a few here on the side and you can these are all pupae, so they look a bit like a rugby ball. And they change in colour from a white one through sort of yellowy-orange to this dark brown and that colour transformation takes place over about eight hours or so.

Georgia - The size of the maggots found, along with the distinct colour changes of any pupae, can give scientists a very good idea of how long a body has been dead for...

Martin - What we do basically at a crime scene is collect the insects. They may be eggs, they may be larvae, they may be actually pupae.  Because, as I say, they wonder away from the body it's essential that at a crime scene we don't just collect the larvae on the body but collect those that have moved away. So we have to dig in the soil around the body and so forth, look under furniture if the bodies indoors and we then age these larvae or pupae in relation to the temperatures at the crime scene.

We actually employ that in a public event we have here called Crime Scene Live.  Members of the public come along on a Friday evening and join us in investigating a mock crime and we're actually able to use some of our latest cutting edge techniques here - CT scanning.  CT scanners are bits of apparatus that you commonly see in a hospital for looking inside your body and we can do exactly the same thing actually with much better resolution.  But we present these pictures to the public and we give them examples of pupae that were collected at a crime scene, and they have to try and work out how old the pupae are, and we think we can get to the resolution of about 10% of the age of these insects.

Georgia - Mmmm. Telling you about how long a bodies been there, that sounds like it can be quite important in the police establishing their timeline?

Martin - Yes, exactly, yes.  I mean, I've worked on about 170 cases with the UK police force now, and I've worked out about ¾ of them the major police question is "how long has this body been dead for?"  But there are other things that could be informative from insects. I mean, insects are ubiquitous in our environment so they're commonly encountered at a crime scene, Like all animals, you are what you eat, and these insects are obviously feeding on a dead body and they can actually ingest the substances in and on that body.

So, for example, they can ingest drugs that a person may have died of an overdose for example. The larvae can actually be collected and ground up and you can find the drugs in them. That might sound a bit ridiculous to say if you've got a body there, but sometimes there might not be a body there and we've worked on cases where a load of fly puparia were found. But the police were suspicious, and the pupae were ground up and inside them they detected drugs.  They then looked for human DNA, and they got a 75% match with a missing known drug user and, with that evidence, they were able to secure a conviction for the murderer. He'd disposed of the body but he'd forgotten to dispose of the insects that were feeding on the body.

Georgia - Ahh some nasty stuff goes on, doesn't it?

Martin - Yes, it's incredible actually.  I never expected to do anything like this with my entomological training and it certainly opens my eyes to a part of human activity and nature that I just didn't imagine.


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