By Wendy Barnaby
Insect specialists from the Natural History Museum are currently leaving dead piglets in secret places in London to see how quickly insects infest their bodies. “Our experiments are to build up a database of what happens in London when remains are left out: how differently they compose at different times of year and in different places,” explained the Museum’s Zoe Adams at the Festival of Science on Friday. The work is aimed to help murder investigations. “The police call us, and we give them an estimate of the length of time between the death of the person and the discovery of the corpse,” she said.
“London is such a huge conurbation that it has a really big impact on the environment, even to the extent of changing the weather – which changes what these insects are doing. If it’s 5o warmer in London than outside London, the insects are going to be growing that much faster,” said Adams.
Zoe Adams was giving the BA Charles Darwin Award lecture.
She and her colleagues use piglets which have been unintentionally crushed by their mothers. So far they have left six out in different places, including open pasture, a shady wood, on the roof of a building and inside a room on the 7th floor of a disused office building, with the window ajar.
Corpses go through a known process of decay: bloating, which gives nasty smells and discolouration; then active decay, in which the breakdown is visible; and finally the corpse dries out to leave a mummified-looking bleached skeleton with muscle and hair. These stages take different times – a couple of weeks to years - depending mainly on the temperature. “You get different insects colonizing the corpse at different stages in the decay process,” said Adams.
The piglet left in the disused office in June took 16 days to reach the mummified stage.
In colder December weather, a piglet inside took 27 days to reach the same stage. One on the roof at the same location was still quite fresh after 27 days. “Flies had laid eggs on the corpse but they hadn’t hatched,” explained Adams.
The first insects to colonise the corpse are blowflies. “They arrive within hours and will stay while the body remains moist,” explained Adams. Dry bodies are infested with beetles, and much later, mites colonise the soil where the residue of the corpse has soaked into it.”
Estimating time of death by looking at insects gives a more accurate picture than previous methods. “The traditional method was by rigor mortis, when the body goes stiff,” said Adams. “It peaks after 2 to 3 days and then melts away, so once you’ve gone past three days it doesn’t work any more.”