Insects a biological clock following a murder

Saturday 23 November 2013 12:15PM (view full episode)

A body is found in the forest wrapped in a blanket. Another lies in a suitcase. How long have they been there? As entomologist Martin Hall explains, the presence of insects provides forensic information. Particular insects arrive at particular times during the decomposition of a body. And whether the insects are there in adult form, or juvenile form or as eggs reveals valuable information which can help piece together the time of death.

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Robyn Williams: Of course the classic way to solve a murder mystery is by consilience. Take fingerprints, alibis, bloodstains, motives, separate lines of evidence and put them all together to find out who done it. Martin Hall at the Natural History Museum in London also uses bugs and maggots.

Martin Hall: We worked on a case in 2009, quite an infamous case which resulted in someone called Clinton Bailey getting a life sentence, 30 years in prison. And he murdered a young woman and he was a very nasty person and he used her money, drained her accounts, he actually used her money to purchase a suitcase in which he disposed of her body.

But because we had actually previously been working with people from the Forensic Science Service and only a couple of months before then we'd worked on another body found in a suitcase, it got us thinking about how accessible are suitcases to flies. If you find insects on a body in a suitcase, have they arrived there before the body was put in the suitcase, were they actually able to penetrate the suitcase?

So what this stimulated was we have a collaboration with the Metropolitan Police Service and also with King's College where they are interested in training up the next generation of forensic scientists. And we took on one of the students, Poulomi Bhadra, and she's done some very interesting work now on working out how accessible or otherwise suitcases are to flies.

Robyn Williams: I suppose the whole point of that is to find out how long the body has been in there, and if you get the succession that comes from the laying of eggs and all the rest of it with the insects that will give you a greater clue.

Martin Hall: That's right, yes. Ultimately what we do in forensic entomology, the number one question I'm asked in about 75% of the cases I've worked on is how long has this person been dead for. Of course we have to hold our hands up and say to the police right from the start that we are not saying how long the person has been dead but actually how long ago it was that the insects found the body. And of course there could be reasons why there is a delay, and one of those might be putting someone inside a suitcase. Other reasons are, you know, if a body is found indoors and all the windows are shut and so forth. So there are quite some variety of delaying factors, and bodies in suitcases is just one of those.

Robyn Williams: What have you found out about zips in the process?

Martin Hall: I never knew so many types of zips existed actually, from the ones on your trousers to those on a suitcase, quite different actually, and many zips are much more leaky than others in terms of protection against insects. We've done a lot of laboratory work where we've placed blowflies above zips which below them has been a…similar to a body, it's actually just chicken liver, but anyhow that's suitably attractive to flies. And certainly metal zips, which are quite leaky, the flies lay their eggs on the zips.

What we did though is a proof of concept, we put a pig's head…pigs' heads aren't much loved by the British public so you can pick them up relatively cheaply at a butchers for just £3, and we put one of those inside an airline carry-on suitcase, zipped up with coil zips which are actually very robust and come together leaving hardly any observable gaps unless you look down a microscope. We put this out in our wildlife garden, and there was actually quite a delay in flies arriving, at least 24 hours, 48 hours before we noticed the first eggs around the suitcase. But we certainly saw flies coming in.

We then bought the suitcase inside. We have a room up in our towers which is now not used for anything other than blowflies. And we were able to carry on the work up there. And we got a real surprise about seven days after putting the suitcase out when we found large numbers of maggots crawling around in the sawdust underneath where we had placed the suitcase. And these were actually big maggots and they had somehow managed to escape from the suitcase. The project is still going on and I'm looking forward to dissecting the suitcase to actually work out how they got out. But they had obviously got out, and prior to that they had been able to get in.

We've been able to show that blowflies, they have an ovipositor, the females do, at the rear end, it's a bit like a telescopic aerial on a transistor radio, they can insert this through the gaps in the zips and lay their eggs. And actually if you look at the inside of a zip from the perspective of inside the suitcase you can see stalactites of eggs which have been laid through these gaps in the zips. Obviously those eggs, the larvae that hatch from them are in an ideal position to move onto the body. Not just blowflies, but there are various muscid flies, relatives of houseflies, and big flesh flies as well which we have found developing inside our suitcase. So a lot of activity, it really surprised us how flies and other insects actually can get into the most secure placements.

Robyn Williams: Well, murder hasn't intruded very much into my life, but food in cupboards has, and it's absolutely astounding. A few weeks ago I opened a sealed tube of chilli powder with another lid on top, and there inside were weevils and the bits of webbing that you get, and it's just miraculous. I don't know how on earth they managed to get in there, but food is obviously as vulnerable as you could imagine.

Martin Hall: Absolutely, yes. That's one of the great things about being an entomologist or a biologist generally, your eyes are just open the whole time and amazed by what nature can do. I am a parasitologist as well as a forensic entomologist, so I study insects that don't hang around and wait for you to die, they will infest you while you're still living and infest animals as well. And some of them have the most amazing life-cycle. So there are species of fly that will develop only in the nasal passages of animals, only in the gut, only in the tissues, and some of them are so specific.

My favourite is the rhinoceros bot fly, this will only develop in the stomachs of rhinos, and that was a very good strategy before humans came on the scene with guns and so forth because no one is going to mess with you inside the guts of a rhino. There's a constant supply of food, constant warmth, so it's a very good strategy. But unfortunately this fly, named Gyrostigma rhinocerontis, it's a magnificent fly, and I feel very privileged to actually have seen a live one because most people have never seen the adult flies. They are in such low numbers now that it's a potential example of co-extinction with the rhinoceros. Fortunately rhino numbers have stabilised, but there are only about 12,000, and so the numbers of these flies are probably less than 2 million in any form, maggot or fly, which is trivial numbers in terms of flies.

Robyn Williams: Yes, first find your rhino. But going back to those forensics and those dead bodies, you still need insect evidence to give you a finer backup to an estimate of time of death.

Martin Hall: Yes, it can be really valuable in certain cases. Pathologists are very knowledgeable about the human body and what happens after death, but even they struggle once you get beyond about three days after death because the changes are so variable in decomposition. But insects really are like biological clocks, and as long as you take into account the developmental temperatures, then you can come up with very robust estimates of how long it is that those insects have been on the body.

Robyn Williams: And it's very interesting that when Martin Hall started in forensics 20 years ago there was only one bluebottle species in the UK. Now there are many more. And so just as cutbacks hit forensics, so their contribution can be more valuable and cheap. Martin Hall is a research entomologist at the Natural History Museum in London.


Martin Hall
Research Entomologist
Department of Life Sciences
Natural History Museum
London UK


Robyn Williams
David Fisher

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