This month, Deputy Keeper of Natural History, Emma-Louise Nicholls, takes a look at the crime scene investigators of the animal world.
Two Sides to the Coin
It will probably surprise you to hear that the house fly is critically endangered. Just checking you're paying attention… no it won’t surprise you to hear that the house fly is actually thought to be the most common animal on the planet. But don’t let that make you think they’re not special in their own way; humans are also (seemingly) everywhere and we all have at least a few of those we think are pretty great. The house fly may be numerous, and irritating at picnics, and yes, they can carry many disease-causing pathogens including typhoid, cholera, and leprosy, but they have many upsides too.
This housefly specimen on display in the Natural History Gallery is a model approximately 30 x life-size.
The Scientist Fly
If CSI Miami was made into a cartoon with insect characters, it would seem reasonable for a mosquito to play a blood sucking lawyer. The house fly, on the other hand, would definitely be the cool-guy crime scene investigator. In the real world, the discipline of Forensic Entomology uses insects and the stages of their development to glean clues from fatal crime scenes that can aid legal investigations. If the body is found immediately after death, pathology-based methods are used. However, if the body isn’t found until a day or more later, insects are one of the most reliable indicators of many aspects of the crime.
The decomposition of a body can be split into five phases. Just in case you’re reading this over dinner, I shan’t use the precise medical terms, but they are as follows:
• Could be sleeping (1-2 days)
• Resembles a flotation device (2-6 days)
• Nose peg required before approach (7-12 days)
• Starting to become part of the environment (13-23 days)
• Could be in a museum (24 days onwards)
Flies appear at a dead body very quickly. Some particularly well organised and highly motivated species detect the expiration and land within minutes. As different insects arrive at different stages (listed above), a forensic scientist can use a survey of the species present, and the point at which they are within their life cycle, to accurately establish how long ago the unfortunate person began sleeping with the fishes. In our insect cartoon, our humble house fly is never late to dinner. It likes to get there early in the event, and will land at the point the cadaver starts to resemble a flotation device. There is so much to talk about on this subject and it is extremely interesting, but I’m already going to run out of space so I shall leave it to you to investigate further.
Rather than including an image of flies on a cadaver, as would be appropriate for this point in the blog, I thought you would rather see our beautiful housefly robot from our current exhibition Robot Zoo. This fellow is 200 x life-size!
Flies or Armageddon
Entire ecosystems of wildlife live in urban areas because we produce so much rubbish. You just need a bank holiday to realise how much we rely on refuse collectors and their trash squishing trucks, when they haven’t been for a week it only takes a strong wind or a couple of foxes for the streets to look like Armageddon overnight.
Whilst bin boys and girls kindly collect our rubbish and hide it away where we can conveniently forget about how much food we ate over the weekend, it takes other much smaller members of the animal kingdom than humans to break it down. The housefly is amongst those that aid the decay of organic matter and with every fly that vomits onto the waste food in order to digest it, these insects elegantly ensure our food waste is re-harnessed by the natural circle of life. Thank you flies.
(Muscidae) typically visit the remains during the bloated stage of decomposition (Joseph et al 2011).
PennState College of Agricultural Sciences
The Forensics Library