Entomology in Criminal Investigations - Lab Report Example

Entomology in Criminal Investigations History Scientific research into the of the insect invasion of corpses, especially by blow fly larvae,is well established. Scientific papers were published first in the1880’s and 90’s, by J.P. Megnin in France. However science has been slow to consider arthropod evidence in many cases. Often maggots etc were simply washed away from a corpse before a post mortem took place in earlier more unenlightened times. Pathological methods Other pathological methods such as taking body temperature become useless as time passes, especially after the first 5 days post death have transpired. The police may be concerned with skid marks, gunpowder patterns, causes of arson and all the rest. But there are certain crimes where a knowledge of entomology is invaluable, providing that the pathologist concerned is aware of its limitations e.g. an insect’s development can be affected by a number of factors such as heat, water, fire etc. Also the time necessary before eggs are deposited will vary according to the species and may also be affected by the fact that groups are genetically and geographically different e.g. results in an English winter will be very different from those in a Florida swamp even if the species concerned is the same. Certain species of fly prefer urban, rather than rural environments, so for instance a body found invaded by such fly larvae in a rural situation may well mean that the person was killed in the city and the body subsequently dumped. Jerry Butler, an American forensic entomologist, reports that he uses mainly evidence from five species of flies, in his investigations. Taxonomy originally referred to the identifying and naming of living organisms, and the system of doing this in a scientific way was originally devised by Linnaeus though the system has been much expanded since . Butler claims that if particular flies are found and identified correctly and the ambient temperature is known then the time of death can be determined fairly exactly if the body is found quickly enough. The successful investigation may depend upon the correct analysis of material evidence found and in a case where a body has been undiscovered for some time this will include entomological evidence e.g. have fly eggs been laid and had time to hatch? In case II ( see appendix)the forensic entomologist was able to work backwards from the time that adult flies emerged in order to discover when the first eggs were laid. In Case I ( see appendix) the instars were at stage 3 i.e they had at least 1517 accumulated degree hours. In the case of the child behind the stove the creatures were fully developed Knowing the times that takes may lead to being able to pinpoint the time the body was left on the site ‘providing that the evidence is properly collected, preserved and analysed by an appropriately educated forensic entomologist’ - according to the American Board of Forensic Entomology. However it must be said that after the first week the possibility of error increases as time passes. Some species can detect and invade a body within as little as ten minutes of death. The development of their maggots is temperature dependent as they are cold blooded by nature. The lower developmental threshold for a creature is the temperature below which it cannot develop. There is of course a corresponding higher developmental threshold. The total amount of heat required for a specimen to move from one stage of development to another can be calculated. The letter D in the following diagram refers to degree days of heat units. One degree day is a period of 24 hours with the temperature one degree above the lower threshold. Degree Days of Heat Units. Greenberg ,1985, described how fly rearing data from laboratories could be used to determine such accumulated degree days and hours. Collection of Specimens Please see appendix 1 Toxicological Investigation A body can quickly decompose in certain circumstances and the absence of bodily fluids would make a toxicological investigation difficult or impossible, but insects will have absorbed any drugs or poisons as they digest the flesh that ingested the chemicals prior to death, and so can provide necessary toxicological evidence. Crime scene Investigators All this being said many crime scene investigators have no specialised knowledge of entomology. In order to help them police forces need to have available laminated cards with details and photographs of species to be noted. They must include actual size silhouettes of the creatures so that the investigator knows what to look for. They must be educated in collection techniques and suitable equipment must be readily available. A site, such as that of the Australian Museum on decomposition, shows very clearly the succession of insects that may be found at a crime scene. Animal behaviour Many arthropod species are attracted by the presence of a dead body. It is perceived by them as a major food source for them and their offspring, a nursery and even a home. At the various stages of decomposition different creatures will feed, live on or breed on flesh – different species preferring different stages of the process i.e. the bloated early stage, the ensuing fermentation and finally the dried out body or skeletal remains. Most species stay with a body for only a relatively brief period, to be replaced by others. This is known as faunal succession. See appendix IX. Calculating the stage reached leads to an accurate estimate of when insect invasion began. This cannot always be related to the interval since death as a body may have been stored for at least part of the time in a situation where insect invasion would be impossible or very restricted e.g. in a freezer or wrapped and sealed in plastic. In this case the succession will be interrupted. The pathologist needs to be aware of what would be a normal pattern of insect invasion in a particular habitat. Only then will he be able to note times when this normal situation is not present. Other ways in which a knowledge of entomology can be useful are as when intense insect activity in one area leads to the realisation that there is a wound in that area as this would be the first place where blood was exposed to the insects long before other decay took place. Also heavy infestation in limited areas may be evidence that a person has been abused, raped or bound as this may produce bodily fluids or faeces that are more attractive to insects than clean skin and creatures that would not normally be present will be found. Other factors It need not be linked entirely to the body. Food present at the crime scene may be affected by maggots in the same way. The place of death can sometimes be determined if the flesh is found to have been invaded by creatures that live in a restricted environment e.g. flies that live in sand or leaf mould, found on a body stored in a garage with a clean concrete floor. Most insects that are important to the forensic pathologist have evolved a complete rather than a gradual development which is the common way that insects develop. In this method of growth an egg becomes a larvae and by successive moulting it grows until it enters the pupae or dormant stage and then the adult will eventually emerge. This type of step by step development is called holometabolous. These larval stages are quite different in appearance from the adult creature. The larval stages of various fly species ( diptera) are difficult to differentiate. They all tend to be lacking any legs, and are usually creamy white in colour and soft bodied . If an adult fly has emerged the pupae will look as if it has had one end sliced off and knowing the time needed to reach this stage of development can be an important factor. The early stages of beetles (coleoptera) vary in colour, shape, thickness and hairiness. Some have armoured plates on their backs of various shapes. The cockroach, blattodea, has strong jaws and is capable of damaging human skin. The marks appear as tiny pits. They are also attracted by hair and often remove entire hair shafts if time allows. Apart form a species found in China, they are disturbed by the presence of light and so can be difficult to trap. Forensic experimentation and developments Scientists make experiments of course, as when corpses were set on fire and then the invasion of the site and bodies by various creatures was recorded over a period of time. Also mentioned in the same report ( see’Antenna’ below) is the study of the invasion of dermestid beetles on human corpses over a three year period. Such experimentation may seem distasteful to some, but is necessary if crime scenes are to be interpreted correctly. At a meeting of the European Association for Entomology in 2004 there was concern that properly qualified scientists are not being trained. The report mentions that in some European countries this kind of work is being done by amateurs. Such people are often called upon to decide the post-mortem interval i.e. the time since death, but in fact they can only truly reflect on part of this period i.e. the period of insect infestation, technically referred to as ‘time since colonisation’, which may begin some days, or even longer, later depending upon individual circumstances. Recent developments mean that insects can be identified by their DNA and blood consumed by them can also be recovered form their digestive tracts and linked to humans. Case histories illustrating various stages after death These will be found as appendices. Appendix VI The person had been dead a few days, and some maggots were present. Appendix VIII Internal organs preserved Appendix IV Partial putrification Appendix VI Total putrfication into a greasy mess + a skeletonised skull Appendix V Partial mummification had taken place. The Future As data accumulates in this relatively new field it will become ever easier to define what and when has happened. However each case is different and new challenges are there to be met. Books and Journals Adams Z and Hall, M. ‘Methods used for the preservation of blowfly larvae and their effects on post-mortem larval length.’ Forensic Science International 138: 50 – 61, 2003 Ames, C and Turner, B. ‘Medical and Veterinary Entomology’ 17: 178 – 186, 2003 Beneke, Mark, ‘Meeting Report’ of the European Association for Entomology, in ‘Antenna’ Vol 28 (3):169-171, 2004 Byrd, J. and Castner, J. ‘Forensic Entomology: Insects in Legal Investigations’ CRC Press, Florida, 2001 Electronic Sources Meeting of the European Association for Forensic Entomology, Lausanne, Switzerland, April 2005. http://www.benecke.com/eafe_abstract_2005.html retrieved 13th March 2007 Open Directory Project http://dmoz.org/Science/Biology/Zoology/Arthropoda/Entomology/Forensic_Entomology/ Dr Zeno’s Forensic page http://forensic.to/links/cgi-bin/search.cgi?query=entomology&mh=25&type=keyword&bool=and retrieved 13th March 2007 Mark Beneke, forensic scientist http://www.benecke.com/antenna.html retrieved 13th March 2007 http://wiki.benecke.com/index.php?title=Forensic_Entomology retrieved 13th March 2007 Australian museum online http://www.deathonline.net/decomposition/corpse_fauna/index.htm retrieved 13th March 2007 University of California news http://www.ipm.ucdavis.edu/WEATHER/ddconcepts.html retrieved 13th March 2007 University of Florida News httphttp://www://news.ufl.edu/2001/03/29/maggots/ retrieved 13th March 2007 University of Missouri, American Board of Forensic Entomology. http://www.research.missouri.edu/entomology/chapter1.html#history retrieved 13th March 2007 Appendix 1 Collection of Species The collection of species and of data from a crime scene can disturb a corpse, as when the ground beneath or surrounding a body must be investigated and so there is need to co-ordinate the work of the scientist with the person in charge of the investigation. Before the collection takes place notes should be taken of such factors as any localised micro-climate, the weather conditions and the general habitat, the effects of sun, shade, open doors or windows etc. Such work is sometimes referred to as Medicocriminal Entomology and will be recorded on a ‘Death Scene Form’. One writer, Mark Beneke, refers to it also as ‘forensic arthropodology’ The exact forms used will vary according to the local authority, but should include such information as to whether the situation is rural, urban or aquatic. Some species will lay eggs in sunlight, while others prefer darkness. Finding the ’wrong’ creatures for a particular environment on a body means that a body has been moved at some stage. The area should be designated as forest, brush, roadside, building – open or closed etc. The state of decomposition as should whether or not the body is clothed and how much it has been exposed to the air. As well as body temperature, and that at the intersection of body and earth, the ambient temperature and that of the soil and larval mass should be recorded. According to Ames and Turner, 2003, low temperatures will delay the development of blow flies. If indoors note whether or not fans or heating are on. There have been cases where air conditioning and fans were left on in closed rooms and then the killer has returned to the scene and opened doors or windows in an attempt to muddy the evidence. All such factors must be balanced with that of the insect evidence. Collection of specimens should begin with that of adult flies and beetles as these are very easily disturbed, and will quickly vacate the scene. They can be trapped in nets or sticky traps and then transferred to killing jars and so then transferred to a vial containing 75% ethyl alcohol. Crawling beetles can be placed immediately in the solution. Labelling should include date, time, location, (including where on the body or in relation to it) the case number and the name of the person making the collection. Eggs and specimens of maggots from the larval mass next. The largest larvae should be sought as these will represent the longest time lapse. Some entomologists prefer boiling, but this can be impossible on site and alcohol is easier to transport and use. Either way the method of preservation should be recorded. Live ones should be captured and placed in suitable aerated containers with either moist paper towels or if possible some meat such as liver or pork. Samples should be taken of top soil, leaf matter etc including specimens from beneath the head , torso and from under the limbs. Macrocheles mites are common at an early stage and will be followed by other types who feed on dry skin further on in time. Moths (Lepidoptera) feed on hair during their larval stage and wasps, ants, spiders and bees may feed on larvae – this latter may cause problems if they have eaten most of the fly larvae before a body is discovered. Appendix II Average Minimum Duration of Developmental Stages and ADH for P. sericata 22 Degrees C 29 Degrees C Hours ADH at End of Stadium Hours ADH at End of Stadium Egg 23 506 18 522 1st Instar 27 1100 16 986 2nd Instar 22 1584 16 1450 Feeding 3rd Instar 22 2068 22 2088 Postfeeding 3rd Instar 108 4444 94 4814 Pupa 143 7590 130 8584 Appendix III Average Minimum Duration of Developmental Stages and ADH for Phormia regina at 22 Degrees C Hours ADH at End of Stadium Egg 20 440 1st Instar 25 990 2nd Instar 25 1540 Feeding 3rd Instar 25 2090 Postfeeding 3rd Instar 125 4840 Pupa 116.5 7403 Appendix IV The child behind the stove On 21 May 1947 the police found the body of a child behind a stove in a farm at St. Hubert (Belgian Ardennes). The body was wrapped in a linen cloth in which, at the time of the discovery, there was numerous larvae of Calliphora vicina Robineau-Desvoidy in the final stages of their growth; in addition there was a dead female of C. vicina (which had died during hibernation after laying eggs), a quite recent pupae of the same species and some pupae of Phoridae. The Calliphora larvae had nibbled at the face of the child, causing the disappearance of the eyes and skin; they had penetrated into the frontal sinuses and from here had devoured the brain. The neck and the upper parts of the arms, as well as viscera, were also severely damaged. The larvae of Calliphora produced all their pupae between 21 May and the evening of 22 May; the adults appeared from 2 June onwards, perhaps ten days after pupation. J. & M. Leqlerq had earlier reared numerous specimens of C. vicina and had been able to determine with the greatest precision that during the spring under the thermal conditions of a lightly warmed room, the temperature of which had never exceeded 20 degrees Celsius, and under good nutritional conditions on fatty cheese, the development of a batch of eggs of Calliphora required 19-20 days from the day when the eggs were laid to the formation of the first pupae. One can suppose that the larvae found on the corpse underwent development under comparable conditions because (1) they developed in the spring, (2) the corpse had been left behind the stove which was sometimes lit, and, consequently, the temperature conditions should have been appreciably like those of a lightly warmed interior room, all the more so, because the month of May 1947 was relatively warm. The Leqlerqs had excluded the hypothesis that the larval development had been accelerated by temperatures higher than those in their experiments, because the stove had not been alight all the time and it was evidently sheltered from the rather exceptional rises of temperature on some of the days in May 1947. They therefore agreed that there was a strong presumption that the eggs had been laid some 20 days before 21 May, perhaps about 1 May 1947. Moreover, eggs laid by Calliphora must have been laid on the corpse a short time after it had been abandoned. In fact: Calliphora vicina is common throughout the year, present in rural houses and passes the winter in the adult stage. The females very readily detect the odour of flesh that is beginning to decompose. As it was a case of a corpse abandoned in the open air at a time of the year favourable to rapid putrefaction, only a few days would have been needed before the first blowfly arrived to lay eggs. It is known that Calliphora belongs to the first wave of necrophagous species, which colonize a corpse in open air. It was the first generation of Calliphora, which had been able to develop on the corpse. Every earlier generation would have left traces such as empty puparial cases under the corpse or in the cloth covering it. Therefore they formed the hypothesis that the corpse was placed where it was during the last week of April, al little after the murder of the child. The judicial inquiry took its course and the culprit was arrested; his declarations and confessions completely confirmed the Leqlerqs conclusions. Appendix V Case 6 BACKGROUND INFORMATION The decomposed body of a woman was discovered in the "kitchen" of the first floor of a house in a small Pennsylvania town on Aug. 26. From the accounts of the neighbours, this woman was a hermit, who lived by herself. She did not have a job, and as the home she lived in was large, she had reputedly had the utilities to the house turned off several years previously, to save money. Quite possibly she was mentally ill, as for many years she had kept her face covered with a shawl when in public, even at the height of the summer. She supposedly walked several blocks to the post office to get her mail every weekday. The body was discovered by the man who lived across the street. He forced his way into the house through the front door at the request of some neighbors, who were complaining about a strong smell. I saw the body on Aug. 27, and was told that it had not been disturbed. It was lying on its back with the head pointed toward a door leading to a garage, and the right hand lying on the chest. The feet pointed towards what was once a dining room. As befitted the womans eccentric habits, the windows were covered with screen on the outside and plastic on the inside, probably to retain heat. This covering formed a tight, fly-proof barrier. The lady had piled furniture and trash up to the ceiling around the doors and windows in the kitchen and living room, probably also to serve as insulation. Because of this trash, I was not able to examine the door leading from the inside of the kitchen to the garage. The external garage door, however, did not fit the ground tightly. The smell from the body emanated from a crack between the bottom of this door and the ground. This smell had attracted a large number of blow flies, which were buzzing around the opening. It was likely that flies had unimpeded access from this opening to the body. The house was extremely dark inside, and we had to use flashlights to see. The "kitchen" where the body was found was darkest of all. Most of the kitchen area was occupied by what looked like a low bunk bed. Trash, food, and cardboard were stacked on top of and around three sides of the bed. This formed a sort of cubby hole that apparently formed the normal sleeping quarters for the dead woman. Her body was lying on the floor next to the "bed." Most of the head tissues had been eaten away by maggots. What was left of the head seemed to be slightly mummified. Other than the head, most of the womans body seemed to be intact. The legs in particular did not seem to contain any maggots or other insect larvae. The maggots near the head had formed a large "mass" to the right side of the neck. This mass was about 2-3 inches deep. A similarly thick mass of maggots was present on the surface of the womans clothes near her mid-section. A few adult flies were trying to get out one of the windows. A few rove beetles were also crawling on and under the body. I collected maggots from the two large masses at about 4 PM. I put some maggots in each mass in alcohol and I kept some alive to rear through to adult flies. I also took the temperature and relative humidity inside the house. While I was present (3-5 PM) the temperature varied from 71-72 degrees F and the relative humidity from 63-66%. The temperature outside in the sun was 84 degrees F. All of the maggots in both masses were large and moving about vigorously. They did not appear to have yet reached the stage where they began to pupate. I did not see puparia around the body. There was so much trash in which the puparia could be hidden, however, that this absence in itself was not conclusive. While I was in the house, I collected 8 live adult blow flies from the window of the dining room. I later pinned and labeled these flies, and examined them. I was looking to see if they were "teneral," i.e., if they had a soft, flexible exoskeleton that flies have a day or so after emerging from their puparia. They were not teneral. I therefore do not believe they developed on the body. Instead, I think they flew into the house from the outside, attracted by the smell. They proved to be the same species that I eventually reared from the maggots. HOW I IDENTIFIED THE MAGGOTS I identified the maggots by rearing them through to adult flies. Adult flies are easier to identify than maggots, because they are much more complicated. Identifications using adults are also more reliable than those using maggots. When I collected the maggots I placed them into half-pint canning jars on top of some crumpled, damp paper toweling I had put inside. I sealed the jar using the original canning jar "ring," screwed-on over a circular coffee filter measuring 8 inches in diameter. This arrangement kept the maggots moist but allowed them to breathe. When I got home, I removed the coffee filter from each jar and placed several small pieces of beef inside on top of the damp toweling. This beef was purchased pre-cut and was originally intended for fondue. I then placed each half-pint jar in a larger "rearing chamber," or plastic container with a small opening at the top to allow air to enter. This opening was covered with both screen and with paper from a coffee filter. The rearing chambers were checked at intervals for the appearance of puparia. They were kept at a constant 77 degrees F (25 degrees C) and 50-60% relative humidity. For each puparium or group of puparia I found, I recorded the date and time. As I proceeded I sequestered the puparia or groups in separate chambers. These chambers were examined at intervals for the appearance of adults. When adults were noted the date and time were recorded and the adults removed to the freezer. I was able to rear a very large number of flies using this method--many more than I needed. These flies all belonged to one species, Phormia regina (Meigen). This fly goes by the common name of "the black blow fly" and is a frequent visitor inside houses and at other deeply shaded locations. It has even been recorded as laying its eggs at night (Greenberg, 1990). I retained 20 of the flies as pinned specimens. Ten of these emerged from maggots collected near the head, and ten emerged from maggots collected on the stomach. Each fly was pinned over the puparium from which it emerged. The important information from these rearings is 1) when the first flies emerged, 2) when the last flies emerged, and 3) if there was any concentration of emergence, i.e., did most of the flies emerge at any one time. This data is given below. H = Maggot collected from head area, S = Maggot collected from stomach area. It can easily be seen that most of the flies from both head and stomach regions pupated on 30 Aug. and emerged as adults on 4 Sept. HOW I DETERMINED WHEN THE FLY EGGS WERE LAID To determine when the eggs were laid that gave rise to the flies I reared, I worked "backwards" using the concept of Accumulated Degree Hours (ADH). ADH is a developmental concept, and is meant to portray how much thermal input an insect requires to complete its development. Insects, like most other animals, have an optimal range of temperatures for development. Most insects cease growing when the temperature drops to near freezing, and die at some temperature below this. Likewise, if the temperature rises, at some point an insect will cease development and then die. The ADH is nothing more than the temperatures in-between these "stop" points, that is, the optimal temperatures for growth, added up for the life of the insect on an hourly basis. The ADH required to reach any one stage in the life history is thought to be fairly constant for most blow flies, regardless of whether this ADH was reached under constant or varying temperatures. Greenburg (1991) listed the number of hours required to reach various life stages for Phormia regina at 22 degrees C. This is fortuitous, as 22 degrees C is the same as 71-72 degrees F. This was the temperature of the house when we collected the maggots. My first step was therefore to take Greenburgs data and construct the following chart. This chart shows the number of ADH needed to reach the end of each stadium, or period in the life cycle of P. regina. The ADH in the chart were obtained by multiplying the number of hours given by Greenburg by 22 degrees C. Average Minimum Duration of Developmental Stages and ADH for Phormia regina at 22 Degrees C Hours ADH at End of Stadium Egg 20 440 1st Instar 25 990 2nd Instar 25 1540 Feeding 3rd Instar 25 2090 Postfeeding 3rd Instar 125 4840 Pupa 116.5 7403 I believed that we could not do better than use this temperature as a constant to figure the ADH, i.e. to set the temperature arbitrarily at this value for the week or two preceding the discovery of the body. Normally, I would try to find a nearby weather station. I would then use the hourly temperatures they had recorded. But in this case the only weather station was about 20 miles away. And the station would only record the outside temperature. That there was little relation between the temperature outside in the sun and the temperature within the house was shown by the difference I measured between the two (84 degrees F outside vs. 72 degrees F inside). I also did not feel that the temperature at the death scene varied much between day and night. The house was well sealed and the kitchen was full of papery trash that would have acted to stabilize fluctuations. Using a constant 22 degrrees was the best we could do. As you can see from the chart, at 22 degrees C, Phormia regina requires an average minimum of 7403 ADH to develop from a freshly laid egg into an adult fly. I used this last figure to begin working backward. I matched this average ADH with the average time our flies took to emerge. Most of the flies I reared emerged as adults on Sept. 4. About as many emerged before as emerged after 12 noon. So I used 12 noon as a rough starting point. The maggots were collected on Aug. 27 at about 4 PM. During most of the time between Aug. 27 and Sept. 4, they were kept at 77 degrees F or 25 degrees C. This interval thus amounted to 188 hours, which, when multiplied by 25 degrees C, gave 4700 ADH used. This leaves 2703 ADH that must have been used prior to my collection. 2703 ADH divided by 22 degrees C is equal to the number of hours this would have taken, or 123. Thus the majority of the eggs were laid 123 hours--5 days and 3 hours--prior to 4 PM on 27 Aug. MY CONCLUSIONS My conclusion is therefore that the majority of eggs were laid on the body during the daylight hours of 22 Aug. It is likely that death occurred sometime the night before. This conclusion is based on the premise that one or more flies were either already present in the house, or that they had unimpeded access to the kitchen through the garage. I think one or the other of these possibilities is extremely likely. LITERATURE CITED Greenberg, B. 1990. Nocturnal oviposition behavior of blow flies (Diptera: Calliphoridae). Journal of Medical Entomology 27:807-810. Greenberg, B. 1991. Flies as forensic indicators. Journal of Medical Entomology 28:565-577. Appendix VI Case I BACKGROUND INFORMATION The body of a middle-aged male was found in a weedy lot at about 1 PM on a hot day in July. The lot was immediately behind a business in the very middle of a small town in the northeastern United States. The man had been beaten to death. He had also apparently been lying in the lot for several days, as a number of maggots were observed on the body. The coroner, who was at the scene, collected some of these maggots at this time. I used them for the analysis that follows. The body was taken to the morgue at about 6 PM, and placed in a drawer. Additional maggots were collected and placed in alcohol between 8-9 PM the next day, during the autopsy. No maggots were collected for rearing because at the time of the autopsy the body had already been treated with insecticide. THE IDENITY OF THE MAGGOTS I chose the largest maggots from the sample collected when the body was found. I picked the biggest individuals because I figured they were the oldest of the lot. I mounted them on microscope slides to facilitate their identification using a microscope. I mounted eight of the maggots on slides. Four of these maggots turned out to belong to the blow fly Phormia regina (Meigen), and four to the blow fly Phaenicia sericata (Meigen). The cephalophyrngeal skeleton (mouth hooks) and posterior spiracular openings (breathing holes) were dissected from one specimen of each species to facilitate identification. These structures could be seen in the other specimens as well. The rest of this analysis will be based on the maggots I mounted belonging to Phaenicia sericata. A great deal of information is available on the development of this species. HOW I DETERMINED WHEN THE FLY EGGS WERE LAID The first thing I needed to do was to determine what instar the large maggots of Phaenicia sericata were in. An "instar" is a method of referring to a period of growth in the life history of a larval insect like a maggot. It is the period of time between two molts, i.e., the period of time after the larva has shed its skin and before it sheds it again. Maggots shed their skin twice as they grow. The time between hatching and the first shed is called the first instar; the time between the first and second sheds, the second instar; and the time between the second shed and the transformation into a pupa, the third instar. The large maggots I examined were all third instars. They were third instars because they 1) possessed anterior spiracles (breathing holes) and 2) had posterior spiracles with three slits (Liu & Greenberg, 1989). First instars lack anterior spiracles, and second instars have posterior spiracles with only two slits. These features were clearly visible in the slide-mounted specimens. The fact that these large maggots were third instars meant that they took at least 1517 "Accumulated Degree Hours" or ADH to develop. The ADH required to reach any one stage in the life history is thought to be constant for most blow flies, regardless of whether this ADH was reached under constant or varying temperatures. Phaenicia sericata, however, is an exception in that the rate of development is proportionally slower at higher temperatures. Greenburg (1991) listed the the number of hours required to reach various life stages for Phaenicia sericata at two constant temperatures, 22C and 29C. I took this data and constructed the following chart, showing the number of ADH needed to reach the end of each stadium. Average Minimum Duration of Developmental Stages and ADH for P. sericata 22 Degrees C 29 Degrees C Hours ADH at End of Stadium Hours ADH at End of Stadium Egg 23 506 18 522 1st Instar 27 1100 16 986 2nd Instar 22 1584 16 1450 Feeding 3rd Instar 22 2068 22 2088 Postfeeding 3rd Instar 108 4444 94 4814 Pupa 143 7590 130 8584 You will notice that the total ADH required to reach adulthood is higher at 29C than at 22C. This difference was very important, because it meant that I had to somehow adjust my analysis to one or the other set of figures, or find some way to interpolate between them. I chose the latter course. During the three days prior to being collected the maggots developed at an average temperature of slightly over 25C--a figure which falls nearly halfway between the two temperatures Greenberg studied. The ADH figures I used for the analysis were therefore averages of the figures in the above chart for 22C degrees and 29C. To use my first ADH as an example, the 1517 mentioned above is halfway between 1584 ADH, which the maggots take to become third-instars at 22C, and 1450 ADH, which they take to become third instars at 29C. I used this figure of 1517 as a base on which to build the minimum ADH required for the development of the large maggots I mounted on slides. Since my particular maggots were well along into the third instar, I needed to derive an ADH figure to add to 1517 to account for this extra development. That is, I needed to know how long the maggots had been third instars. This was a very important question. The third instar is a very long period for maggots. The maggots of Phaenicia sericata spend an minimum of 116 hours (nearly five days) as third instars at 29C (Greenberg, 1991). Fortunately, the time encompassed by the third instar can be divided into two portions, as indicated in the chart. The first portion of this instar is spent feeding and growing, and the second portion is spent wandering about looking for a site to pupate. The second portion is about four times as long as the first. In the figures given above for the development of Phaenicia sericata at 29C, for example, the first, feeding portion of the third instar lasts a minimum of 22 hours, whereas the second, wandering portion, lasts a minimum of 94 hours. These two phases of the third instar can be distinguished by the size and color of the crop, an internal sack between the mouth and the stomach of the maggot. This sack can be seen through the skin of the maggot. It is bright red in feeding maggots. The maggots I mounted on slides had crops that were bright red. Thus they were feeding third instars. The red color disappeared in the mounted specimens because I removed all the body fluids in the slide-mounting process. But the red was still visible in some of the smaller specimens left in alcohol. I kept these specimens in case they were needed as evidence. Now that I knew my third-instar maggots were feeding, I needed to know for how long. Greenberg (1991) presented two graphs showing the relationship between length and developmental time for all instars, i.e. for the entire time period between the hatching of the egg and pupariation. These graphs are reproduced below: The graph on the left shows the relationship at 22C, and the one on the right, at 29C. As you can see, these graphs differ slightly from each other. On both, however, in the time period covering the early third instar, there is a linear relationship between maggot length and age. Older maggots are longer. I therefore thought I might be able to use the information presented here to find out how long the maggots had been feeding. From the 22C graph, you can see that at the beginning of the third instar, the maggots are just at 8 mm long. From the graph for 29C, you can see that they are somewhat larger, measuring in at slightly over 8.5 mm. At both temperatures 22 hours later--that is, when they stop feeding--the maggots are approximately 14 mm long. I took these figures and from them constructed the graph below. I then measured the largest maggot I had from the body. Using this length with my graph, I determined the number of hours after moulting into a third instar it would have taken this maggot to have reached its current size. I did this for both 22C and 29C, convereted the figures into ADH, and then averaged the two. Specifically, the biggest maggot I had mounted was 10.58 mm long. Using the graph, for 22C this translated into 220 ADH (10 hrs. x 22C), and for 29C into 252 ADH (8.7 hrs. x 29C). The average of these two figures was 236 ADH. Therefore, the largest maggot could have been no further along into the third instar than 236 ADH. When this 236 was added to 1517, I got 1753 ADH. I then considered this ADH as the minimum required to allow the large maggots taken from the body to develop. The available ADH are listed in the chart below. This chart shows the hourly temperatures for the day the body was found (Day 0), along with those for the three preceding days (Days -1 to -3). These temperatures were compiled by the weather station at an airport, which was about 8 miles from the scene of the crime. On this chart, the figure 1753 falls almost exactly at 70 hours prior to the time the maggots were collected by the coroner. Accumulated Degree Hours Day Hour PMI Temp (C) ADH -3 13 72 29 1815 -3 14 71 30 1786 -3 15 70 31 1756 -3 16 69 31 1725 -3 17 68 32 1694 -3 18 67 31 1662 -3 19 66 30 1631 -3 20 65 28 1601 -3 21 64 27 1573 -3 22 63 26 1546 -3 23 62 26 1520 -3 24 61 25 1494 -2 1 60 25 1469 -2 2 59 25 1444 -2 3 58 24 1419 -2 4 57 24 1395 -2 5 56 24 1371 -2 6 55 24 1347 -2 7 54 24 1323 -2 8 53 25 1299 -2 9 52 27 1274 -2 10 51 28 1247 -2 11 50 29 1219 -2 12 49 31 1190 -2 13 48 32 1159 -2 14 47 33 1127 -2 15 46 33 1094 -2 16 45 34 1061 -2 17 44 33 1027 -2 18 43 33 974 -2 19 42 32 941 -2 20 41 26 909 -2 21 40 23 883 -2 22 39 23 860 -2 23 38 21 837 -2 24 37 19 816 -1 1 36 19 797 -1 2 35 19 778 -1 3 34 19 759 -1 4 33 18 740 -1 5 32 18 722 -1 6 31 18 704 -1 7 30 18 686 -1 8 29 19 668 -1 9 28 19 649 -1 10 27 20 630 -1 11 26 22 610 -1 12 25 24 588 -1 13 24 26 564 -1 14 23 27 538 -1 15 22 27 511 -1 16 21 28 484 -1 17 20 28 456 -1 18 19 28 428 -1 19 18 27 400 -1 20 17 26 373 -1 21 16 24 347 -1 22 15 23 323 -1 23 14 22 300 -1 24 13 23 278 0 1 12 22 255 0 2 11 22 233 0 3 10 21 211 0 4 9 19 190 0 5 8 19 171 0 6 7 19 152 0 7 6 19 133 0 8 5 21 114 0 9 4 22 93 0 10 3 24 71 0 11 2 23 47 0 12 1 24 24 0 13 0 25 0 MY CONCLUSIONS In cases like this one that are based on maggot length, a range of about plus or minus two hours is in order (Kondratieff, B. C., 1995). During the summer one can also make the assumption that adult flies will find a body within a few minutes of death, assuming that it is daylight and the body is in the open. My final report therefore said that the largest maggots of Phaenicia sericata developed from eggs laid 68-72 hours prior to their collection by the coroner. LITERATURE CITED Greenberg, B. 1991. Flies as forensic indicators. Journal of Medical Entomology 28(5):565-577. Kondratieff, B. C. 1995. Personal communication. [Dr. Kondratieff is a forensic entomologist at Colorado State University. He has had over 100 cases similar to this one.] Liu, D. and B. Greenberg. 1989. Immature stages of some flies of forensic importance. Annals of the Entomological Society of America 82(1):80-93. Appendix VII Case 3: Cheese skipper larvae on heroin addict A 38 year-old known heroin user committed suicide by lying her neck under the wheels of a moving train at the end of November 1995. The corpse was found under foliage in shrubbery near the track which run through the city. The soft parts of the trunk were reduced to a greasy mash. Organs of the abdominal cavity and the chest were completely disintegrated (fig. 4). A small amount of decayed tissue was found adhering to the pelvis and the extremities. A shock of hair measuring 35x20 cm (14x8 inch) was found near the skeletonised skull. A first estimate led to a post mortem interval of 2-3 months. The body was wearing jeans which were still in good condition. In the autopsy room, within the decomposed mush, but also on the uncovered bones, masses of yellow piophilid larvae of 8 mm in size could be observed jumping up to 50 cm in height or 10 cm aside for more than five hours at 17ºC. On top of leathery dried parts of skin, a nearly closed layer of pale yellow eggs was found; similar eggs were found in the shock of hair. Because the breeding room had been poisoned while breeding the eggs, determination had to be performed by use of single body parts of one adult fly which was determined as Piophila casei LINNÉ (fig. 5). P. casei is a typical inhabitant of freely exposed cadavers three to six month post mortem, i.e. in the third of eight successional waves (1,44). Because single P. casei females lying around 200 eggs, the observation of masses of eggs covering the body led to the conclusion that a first and probably a second generation of cheese skippers had hatched on the corpse. Under good conditions, Piophila eggs develop to adults within 11 to 19 days; together with the information given in (1) and our temperature data (fig. 6) a post mortem interval of 90 days (start of the third wave) plus 22 to 38 days, i.e. 112-128 days was calculated. Later it was found that the woman had been missing for four months. This case indicates that P. casei does not shorten its development significantly under the influence of heroin as was observed for some arthropods (45). However, the exact concentration of heroin could not be determined because of the severe decomposition. Under the shock of hair on the clothing of the corpse, several beetles were found which to our knowledge are not highly specific for a certain state of decay (1,44). We found two adult Staphylinidae (one Oxytelops tetracarinatus which is the most common representative of the genus Oxyteles (GRAV.) and is frequently found in excrement and rotten plant materials; one Philonthus spec.) which on their own are not suitable for estimating of PMI because of their common occurrence on cadavers, e.g. even two years after burial on corpses (1). Furthermore, three adult individuals of the genus Atheta THOMSON (which lives on dry carrion but also on fungi and decaying leaves) and both larvae and two adults of the clerid "red legged ham beetle" Necrobia rufipes (DE GEER) were found. One of the Necrobia larvae immediately burrowed into a piece of gauze, pupated at 17 ºC which is 1 ºC less than its supposed lowest breeding temperature (29) (fig. 7) and hatched out after 54 days. Necrobia rufipes is known to be a late inhabitant of corpses and feeds on dry cadavers (also on mummies and ham) and probably on larvae of other arthropods. The observation of one dead pupa of Fannia (house fly) and the absence of any silphid beetles was without diagnostic value but is mentioned for the sake of completeness. The headless body case Appendix VIII Case 4 In September 1983 the headless body of a young woman was found hidden in gorse and bracken in Devon. Many full-grown larvae and puparia of Ophyra were found in clothing from the body, but only a few larvae and puparia of Calliphora. The absence of significant numbers of blowfly larvae and lack of evidence of their feeding in the natural orifices or gunshot wounds on the corpse suggested that the body had been kept elsewhere, probably indoors, for several months and only recently placed on the site it was found. The good state of preservation of the internal organs (which misled the pathologist to estimate the time of death as 7-10 days), coupled with the presence of Ophyra, suggested that the storage place was warm and dry. The presence of the few Calliphora larvae and puparia suggested either that the body had been on site for some 20 days or so and being in a dry state had only attracted a few blowflies, or that the head perhaps been exposed and available to blowflies wherever it was stored, and removed on site when a few larvae had crawled off onto the body. When the head was subsequently found it contained several larvae and puparia of Calliphora, but only one Ophyra, which suggested exposure and subsequent detachment when the differing maggot populations of head and body were then established. Subsequent confession by the murderer established that the victim had been shot and kept in a sauna room for five months, then dumped at the edge of the wood where the body was found. The head had been removed on site and then brought back and kept in a plastic bag in the boot of a car. Appendix IX Fauna found on decaying bodies ( not an exhaustive list) Calliphoridae Hours after death Scarcophagidae Hours after death Staphylinidae Hours after death Sphaeroceridae Early stages of decay Sepsidae Between caesic decay and ammonical decay stages Brachycera stratomyidae Later stages of decay Acari When fluids exit body Histeridae During drying process Dermestidae Dried body Read More