What bugs will descend on a dead body? Forensic entomologists use the development stages of larvae to work out how long ago the animal or person died. In these insects, the larval stages appear quite different from the adult form as shown in the Forensic Entomology page. Once the larva or "maggot" is finished feeding it will move away from the corpse to find a suitable site for the pupal stage. Then they look a bit like rat droppings. The pupal stage can be really useful to the forensic entomologist. If the adult insect has not emerged, the pupa will appear featureless and rounded on both ends. If it has been right through this stage, the pupal case will be empty. This gives further clues to the date the body was first attacked by flies. Beetles The beetles (order Coleoptera) are one of the largest groups of animals, the most common insect, and they also go through the larval and pupal stages so useful to forensic entomologists. The larvae or "maggots" of a lots of blow fly species look almost identical. The larvae of different species of beetles can look very different. Beetle larvae recovered from corpses can be easily distinguished from the maggots of flies because they have 3 pairs of legs. Fly maggots found on dead meat do not have any legs. The number and appearance of adult beetles that can be found on human remains is huge. You may just be lucky enough to see your local species with the experiment. Cockroach Many roach species have strong mandibles that are capable of damaging the skin on a dead body. These can look like abrasions or chemical burns - just to make life even more complicated for the forensic scientists. Roaches will often consume human hair, even removing entire hair shafts during their feeding. The roach species most commonly encountered in forensic investigations are the American, Australian, and the German cockroaches. And that's just the start to the bugs which can appear! This is a really highly skilled area of forensic science! |
larvae and the pupae of a blowfly species The experiment for Your Task
a piece of lamb flank in a solid bucket The first visitor - a wasp |
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It won't only be insect laying larvae, and roach marks in the meat, which will confront the forensic entomologist. Some insects come and take away the evidence. Ants will be there very quickly if the meat is left somewhere where they might discover it. The piece of meat in these photos was left on the verandah - out of the reach of dogs. The ants were there within an hour. Tiny bits of meat were cut from the small slab and taken away. It was absolutely fascinating to watch through a magnifying glass and the macro lens of a camera. The ant on the left comes from the top right of the piece of meat in the photograph below. |
Meat, 2 weeks later, with some leaves and soil, to mimic a crime scene. |
You will need to design your experiment to take account for all the different sorts of insects - and for the other animals. Dogs won't leave a piece of meat for long! Soil and leaves were added to mimic a crime scene (see left) with a body in a shallow grave. The maggots moved from the meat to the soil to pupate. Record everything that happens as often and for as long as you are able.
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The image is scaled approximately 2 to 1 (depending on your screen and resolution), so the length of the meat was about 60 centimetres. The depth was about 20 centimetres and the height was about 30 centimetres. It was approximately the shape of a rectangular pyramid. Estimate the size of the piece of meat in the mandibles of the ant, and the total size of the meat. It took just on 30 hours for the lot to be gone. I photographed it regularly and nothing else touched it. All taken away in tiny pieces. Approximately how many pieces were cut, carried and taken off to the ant nest which was over 2 metres away. How amazing is this! |
About 6 hours into the mammoth task 30 hours later, and they are cleaning up the scraps. |
