The Typical Life Cycle of a Blow Fly
(NLM, 2006)
Beetles
The beetles are also found on corpses; they are one of the largest groups of animals with a complete metamorphosis, which includes eggs, larva, pupa and adult. The beetle keeps it eggs inside their bodies and gives birth to live larvae. The beetle has a unique type of metamorphosis called hyper metamorphosis, in which the larva changes into different forms as it develops. It eggs hatches into an active, long legged larva. As the larva molts, it changed into a C-shaped larva with shorter legs. Then it molts into a legless instars that does not feed. Finally, the legless instars molt into a pupa with legs and wings projecting from it body. Beetle larvae recovered from corpses can be easily differentiated from maggots as they have 3 pairs of legs and the maggots found on decomposing remains will not have any legs. Once a larva as been identified as that of a beetle, further field identification can be accomplished because of the wide diversity of larval forms. Their body varies from almost white, robust, and hairless to dark brown, slender, and quite hairy. Others may appear almost black and have armoured plates on their back. (Byrd, 2007)
The typical life cycle of beetle
In homicide investigations, the forensic entomologist uses the age and stage of development of the insect present to estimate the post mortem interval or “the time since death”. Based on the factors in a particular investigation, the “time since colonization” may or may not closely approximate to the entire post mortem interval. In either case, a forensic pathologist, medical Examiner or coroner must estimate the post mortem interval and the forensic entomology may assist them in providing information on the “time since colonization” which can be used to substantiate a portion of the post mortem interval.
Forensic entomology uses different techniques in collecting their evidence; this include species succession, larval weight, larval length and a more technical method known as ‘the accumulated degree hour technique’, which is very precise if the necessary data is available. A possible post-mortem movement of a corpse inference can be made by a qualified forensic entomologist. Specific habitats are required for some flies like distinct preference for laying their eggs in outdoor or indoor environment. Flies also exhibit preference for carcasses in shade or sunlit conditions of the outdoor environment, thus a corpse that is recovered indoors with the eggs or larvae of flies that typically inhabit sunny outdoor locations would indicate that someone returned to the crime scene to move and attempt to conceal the body.
Likewise, an altered species succession of insect on a body could indicate wrapping or freezing of the body. Due to the ‘typical colonization time’ and ‘sequence of species’ will be altered if any thing prevents the insects from laying their eggs in their normal time frame. The forensic entomologist would notice this alteration, if they are familiar with what would normally be recovered from a body in a particular environmental habitat or geographical location. Complete absence of insect on a corpse would suggest clues as to the sequence of post mortem event as the body was probably frozen, or sealed in a air tight environment.
Also, circumstances surrounding death (like abuse and rape) can be determined by entomological evidence. Victims that are bounded, drugged or helpless often have their cloth stained with urine or feace; otherwise, they are dressed in bed. Certain species of flies would be attracted by such materials. Furthermore, the presence of the species can yield many clues as to both ante mortem and post mortem circumstances of the crime.
The developments of DNA technology has made it possible to determine an insect species, recover and identify the blood meals taken by carrion insects. An individual’s DNA can be recovered from the digestive tract of an insect that has fed on a human. The presence of DNA within an insect can be used to place suspect at a known location within a definable period of time and recovery of the victims’ blood can also create a link between the suspect and the perpetrator.
Insects recovered from decomposing corpse can also be used for toxicological analysis; due to the big appetite of insect on corpses, the soft tissues and other evidential materials needed for toxicological analysis could be quickly eating up, however, an Entomologist can recover the insect larva and run standard toxicological analyses on them as they would do with human tissues. Since insect larvae’s tissues assimilate drugs and toxins that are accumulated in human tissue prior to death, they can be used for toxicological analysis.
Absolute care should be taking while collecting insect and other arthropods from a death scene because the remaining of a corpse could be disturbed. Thus, careful plans should be made for the collection of entomological evidence. Note should be taken and observation should be made to determine the immediate microhabitat surrounding the body.
At a crime scene, the adult flies and beetles would be the first to be collected because they are fast moving and can quickly leave the scene when disturbed. The adult flies should be trapped with insect net, once they have been netted, they can be easily transferred to a vial of 75% ethyl alcohol. Beetles are collected with forceps or gloved fingers and placed directly in alcohol. The specimens should be properly labelled and care should be taken as alcohol can dissolve the ink, thus, pencil should be used. The collection label should contain information on the geographical location, case number, date and hour of collection, location on the body where removed and name of collector.
After the corpse has been removed, many of the insect that inhabit the corpse would remain where the body has been moved, thus samples would be taken from the place, litters and soil from and under the corpse. A good way of collecting leaf litter is by exposing the upper surface of the soil and then, a separate collection from about the first two or three inches of topsoil should be collected. Each soil collection should be about 4-6 inches square and should be taken from underneath the head, torso and extremities. All soil samples should then be placed in a cardboard container for immediate shipment to forensic entomologist. These collections should be labelled and forwarded to a forensic entomologist along with the insect collected from the body.
Note that would be taken at the scene should include the general habitat and location of the body in reference to vegetation sun or shade condition and it proximity to opened door or window should be noted. A documentation of the location of insect infestation on the body and the stage of development of insect should be taken. Evidence of scavenging or predating should also be document.
Meteorological data would also be collected at the scene; this includes ambient air temperature at the scene taken approximately at chest level with the thermometer in the shade. Maggot mass temperature, ( obtained by placing the thermometer directly into the larval mass centre) ground surface temperature and temperature at the interface of the body and ground (this is done by simply placing the thermometer between the two surfaces) finally, the temperature of the soil directly under the body should be taken, (immediately after the body has been taken away) and the weather data that includes the maximum and minimum daily temperature and rainfall for a period spanning from 1 to 2 weeks before the victim disappeared to 3-5days after the body was discovered.
In this experiment, different specimen forms of larval and pupal stages of development were examined.
The aims of this experiment are to develop our appreciation of forensic entomology; to develop our knowledge on flies and insect - their stages of development and difference characteristic. Also, to develop our understanding on the structure of fly larvae and pupae, and increase our knowledge of the methods used to kill and preserve specimens. Furthermore it helps us develop an appreciation of the degree of the difference between Calliphora (blue bottle) and Lucilia (green bottle) fly larvae and pupae.
The materials used in this experiment includes: low power light microscope, lucilia larvae, lucilia pupae, calliphora larvae, and calliphora pupae.
METHOD
During this experiment, five larvae were examined using a low power light microscope.
The experiment was divided into three: preservation of entomological materials, examination of specimens and the forensic case.
Preservation of entomological materials
Three circles were drawn on an A4 paper, and circles were respectively labelled (a) calliphora (b) Lucilia (c) Case sample.
Forceps were used to choose one larvae and pupae from the Calliphora dishes and placed into a cleaned Petri dish.
Forceps were also used to choose one larva and one pupa from the lucilia dishes and placed into a second Petri dish.
The lids were removed from the Petri dishes and a small amount of boiling water was poured into each lid. (Eye was kept on the larva in the dish, in order to prevent it from escaping)
Forceps was used to immerse larvae in the bowling water for 30 seconds (it stretched out and turn white)
The larvae was then removed from the water and returned to their original dish, then the larvae and the pupae were then immersed in all dishes in 70% alcohol solution.
Now the specimens are preserved.
Examination of specimens
One larva was chosen and placed under low power light microscope, and the focus knob was adjusted on the side of the microscope, until the larva was seen clear.
Then, the structure of each larvae and pupae was examined and the overall structure, the spiracles, the mouth part of the larva and the both ends of the pupae was drawn.
Then the samples were discarded and the Petri dishes were rinsed out.
The Forensic Case.
A SOCO has sent a sample of maggots that he retrieved and preserved at the scene of a murder. Identification of the species was required and also, a determination was to be made as to whether the sample set is consistent with the environment in which the victim was found (in a loft apartment in central London).
Two larvae were chosen from the case sample jar and place into a Petri dish using forceps. Then the samples were examined using a low power microscope and drawings of relevant areas were made. And the samples were identified as either, lucilia, Calliphora, or both.
RESULT
The samples of maggot sent by the SOCO were identified to be one lucilia larvae and one calliphora larva; due to the structure possessed by each maggot matches those of lucilia and calliphora larva during comparison.
Below are diagram of our findings.
DISCUSSION
During this experiment we were able to identify different larva and pupa, at the same time; we were able to compare them with each other, knowing their differences; in terms of their overall structure, the spiracles and the mouth parts. From published information on lucilia and calliphora larvae / pupae and the findings of this experiment, the differences and similarities between the samples lies in their composition, looks, age and their habitat. The calliphora larva tends to have spiracles, black vein-like structure running through it and black dots around it segments. While the pupa has a pointed antenna, with a wider mouth part. The lucilia larva is pink in colour and it has a hook-like mouth and a pointed antenna, similarly the lucilia pupa is pink in colour with wide antenna, but it has spiracles at the mouth part.
Pupas are useful in forensic investigation because they represent the longest developmental time, thus, it is important to be able to identify them among other species. Published information on pupae by Sukontason et al (2007) explained that pupa has their own characteristic, which can be used to identify them out of other insect as generally pupa are similar in appearance, and their colour (light brown) makes it more difficult to identify them. Similar to the findings of the experiment, they found out that blowfly pupa can be identified by their anterior ends and the profiles of the posterior spiracles, which had a unique distinguishing characteristics.
One of the case samples was identified to be a lucilia larva because it structures was similar to those of lucilia larva, as it is pink in colour, it has spiracles and a hook-like mouth parts and pointed body. Comparison of the lucilia larva to published information on lucilia approve the conclusion that one of the case sample was lucilia because of the characteristics and features.
The other sample of the case was identified to be calliphora larva as it possess the features of a calliphora larva. Comparison with published support our conclusion
CONCLUSION
The use of forensic entomology is diverse in the society, for example, it is use for detection of abuse in children and neglect of the elderly. It was also reported that some parent use wasps and bees to sting their children as a form of punishment. Furthermore, entomological evidence has been used to prove neglect and lack of proper care for wounds on elderly under both private and institutional care. It is also believed that the stings or presence of bees and wasps may account for the large number of single occupant car accident that lacks a definitive cause. Accident studies also show that insect cause the top 20 automobile accidents. Thus, insects are important in everyday life and are used to gather evidence.
The study of insect is also important in forensic investigation because it can affect the interpretation of blood spatter pattern analysis. Insects walking through pooled and splattered blood might produce tracking that are not recognizable; thus specks of blood caused by insects might mislead crime scene officer, unless they are aware of the appearance of blood contaminated insect.
In addition, an analyst might be confused by faecal drops in an apartment that is very infected, because the droplets might test positive for human blood. Thus, it is important to recognise and properly document the natural artefact that may occur from the presence, feeding and defecation of insects. Insect are also used to determine country or point of origin. For example, in a case of imported cannabis, insects are used to determine the region of drug.
In conclusion, the experiment was successful because the aims and objectives were met; i.e. we were able to identify and differentiate between the types of larva and pupa, also we were also able to classify the case sample as either larva or pupa and its type.
The experiment was precise because we were able to see the structures of the samples from the low power microscope. It was also accurate because when the result was compared with other published information on similar samples, the results were similar. Thus if the experiment is carried out again following the same instructions, the result will be same or similar.
REFERENCE LIST. (2001) Available at: Accessed (4 Dec 2007)
Bullington, S. W. (2004) Available at: . Accessed (2 December 2007)
Byrd, J. H. (2007) Available at: . Accessed (2 December 2007)
NLM (2006) Available at: http://www.nlm.nih.gov/visibleproofs/galleries/technologies/blowfly.html Accessed (3 December 2007)
Sukontason et al (2007) Identifying fly puparia by clearing technique: application to forensic entomology Thailand, Department of Parasitology, Faculty of Medicine, Chiang Mai University.
