Forensic Scientific Writing 2 Essay

Submitted By excelero
Words: 1066
Pages: 5

Review of the article 'The effects of larval crowding and food type on the size and development of the blowfly, Calliphora vomitoria'

Background information:

When a dead body is found in a crime scene or a dead body is discovered elsewhere it is vital to figure out and estimation of how long has it been since the person died. This is an estimation but it can be a very accurate one which will lead to helpful findings in the future. One way of finding out the PMI is by using entomological evidence retrieved from the body. This varies by the size of blowfly larvae on the body and how much they have developed.

Larval length and size can be used post mortem to collect information which will contribute to the approximation of the PMI and also accumulated degree hours or days is another method which can be used.

Factors such as different drugs, foods or certain illnesses of the body can affect the calculation mentioned above have to be taken into account.


The scope of the experiment is to see how different types of tissue affect the overall size, crowdiness of larvae and size of pupated flies.


Crowded samples is hypothesized that will have low survivability but high rate of development. The size of flies will depend on protein and other nutrient levels contained in the different types of tissue types.


200 flies cage liver, brain and muscle tissue weighing boats


Calliphora vomitoria were developed and maintained in covered cages at room temperature and flies had a supply of granulated sugar and water. Furthermore flies were provided with liver exudate for 4 to 5 days daily due to the fact the protein sources promotes ovarian development.

Liver from pigs was placed in the cage in order for eggs to be laid by the female flies. These eggs were then extracted and left to hatch.

Different number of cultures (number of larvae) were transferred to a piece of pig liver, brain or muscle. Each of these samples were then placed in multi-purpose compost under controlled temperature in order for the larvae to be able to feed in order to pupate.

After pupation, flies were frozen in order to die and the size of female and male flies were noted down. Furthermore the the posterior cross vein was measured and the left wing of each adult was removed from each fly and photographed for evidence.


For the results, the indication of speed at which the flies grow on different types of tissue was obtained through the recording of the time taken for adult flies to emerge from their equivalent puparia. Furthermore the first day of eclosion was noted for all the samples.

Development is seen to be faster in the increased density of larval cultures on liver and muscle tissue. The brain tissue culture is observed to have the exact opposite effect, development decreases. Brain was also the most consumed tissue by the larvae.

In low crowded samples there is a minimal difference between the time taken for the flies to reach adult due to the food being in excess therefore eliminating competition for food.

In the highly crowded samples the brain was fully eaten up therefore leaving the larvae in a depletion of a food source. The liver and muscle crowded samples were not fully consumed and there was an excess of food source.

Larval crowding does have an affect on adult survival rate. Firstly, increasing density also increases the food competition which leads to a lower survivability of flies.

Moving on, increased larval crowding results in the production of adults of smaller size for all sample of tissues.

Development of the flies on liver tissue is observed to be the most efficient and brain tissue being the least efficient. Brain seems to be the least nourishing of all the tissues. Brain contains low protein amounts and high water levels therefore it is quickly consumed but still not providing the correct nutrients required for development. Muscle tissue lies in the middle in terms of…