Most of the species recording in the Garden involves finding out what species have come into the Garden of its own accord, but there are sometimes special circumstances enacted behind-the-scenes to attract certain species to lay their eggs... Poulomi Bhadra explains:
"The Wildlife Garden in the summer is thriving with flora and fauna and provides excellent grounds to study the attraction of blowflies to bodies in suitcases. As part of my Masters project at King's, I am investigating blowfly behaviour and particularly their ability to lay eggs without being in direct contact with a food source. This is part of the research conducted by the Museum’s forensic entomologist Dr Martin Hall in collaboration with the Metropolitan Police.
Even though preliminary experiments have been conducted indoors in a laboratory at the top of the Southwest Tower (where the smell of decomposing chicken liver wafts undetected above the crowd of visitors in the rest of the Museum!), it was necessary to see if the results could be replicated in field conditions.
After several failed efforts to protect the experimental set-ups from the resident foxes - who were evidently attracted to the smell of meat and often stole my experiments - we succeded in a set-up consisting of a dog cage that was enclosed in chicken wire.
Dog cage set-up - weighted down to deter foxes!
Petri dishes containing meat, and sealed by a zip, were laid out in the dog cage and behind-the-scenes in the Garden to see if any blowflies would be attracted to them and lay eggs. As it turns out, populations of bluebottles (Calliphora vicina) and greenbottles (Lucilia sericata) visited the cages as soon as they were placed.
The experiment was collected the next day and white dipteran egg clumps were seen to have been laid on the tape of the zips, which had been moistened by the blood and decomposing fluids from the liver beneath. Eggs were also deposited in between the teeth of the zips and when the baits were dismantled in the laboratory, egg clumps were seen hanging like stalactites on the underside of the zips.
Twenty-fours hours later fly eggs were found laid on the zips
This is possible because blowflies lay eggs through ovipositors, which are located at the end of their abdomen. When laying eggs, this ovipositor extends outwards like a lance and can get inside and through crevices, such as the gaps between the teeth of a zip, so that the female is able to drop her eggs.
Female flies extend their ovipositor into gaps to lay eggs in clumps
Calliphora vicina laying eggs on zips in the laboratory experiemental set up
During the especially high temperatures this summer, most of the eggs hatched within 24 hours and the first instar larvae, 1-2 mm long, crawled their way through the gaps in the zip to feed on the meat below. The eggs collected from these trials were reared to adulthood in the laboratory.The species that oviposited (laid eggs) predominantly was found to be the bluebottle, Calliphora vicina. Only four adults of the greenbottle, Lucilia sericata, were reared from the laid eggs, even though both species were present in the garden and trapped in the RedTop® flytraps hung nearby for collecting wild-type flies from the garden.
In the beginning of August, a different experiment was simulated in the field to study a case scenario: a pig’s head, purchased from a butcher's shop, was put in an airline cabin suitcase and then put inside the wired cage. Flies were seen visiting the suitcase regularly during daylight hours but no eggs were seen until the second day, when a single egg was laid on the cloth seam of the suitcase and near the zip. By the third day, more eggs had been laid between the folds of the seam and the zip and inbetween the teeth of the coiled plastic zip. First instars were seen later, travelling along the length of the zip around the suitcase.
Simulation of case scenario - a pig's head in a suitcase inside the cage, left in this position for 3 days
Flies deposited their eggs in between the teeth of the zip and the crevices of the zip slider and the larvae made their way through the zip to reach the food source inside the case
The suitcase was brought indoors after three days to avoid the malodours from the decomposition permeating throughout the Garden, which was open to the public. On the eighth day since exposure, third instar larvae were seen dispersing from the suitcase, looking for suitable grounds to pupate. When the suitcase was opened the bait inside was found infested with third instar larvae which meant that the adult flies, or hatching larvae, had been able to penetrate the completely closed zip to gain access to the food inside.
The experiment is still under study and we are looking forward to replicating a few more proof of concept studies to establish the potential for delay in egg laying, and to confirm the species that show most propensity of laying on enclosed carrion. The results from this research will have practical value in explaining the presence of larvae on bodies found inside suitcases and will help forensic entomologists estimate a more accurate minimum time since death for the bodies of victims who are disposed of in this manner."
Thank you Poulomi, we have enjoyed your company in the Garden this summer, but I can't look at a zipped suitcase in the same way again...
For more information about this work please see Museum's forensic entomology web page or come to this year's free Science Uncovered event on the evening of Friday 27 September and see our forensic enotomologists in person.