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Indian Journal of Forensic Medicine & Toxicology

Insect evidence in legal investigation

Author(s): H. S. Bhawara, Snehlata Singh

Vol. 2, No. 2 (2008-07 - 2008-12)

H. S. Bhawara٭, Snehlata Singh٭٭

٭ Scientific Officer, State Forensic Science Laboratory, Raipur (C. G), ٭٭ District Hospital, Kapa, Pandri, Raipur (C. G)

Abstract

Insects are important agents in the biological breakdown of corpses and often provide valuable clues in criminal investigations. Forensic Entomology is the application of insect biology in legal investigation system. Insect evidence is particularly useful in establishing the time of death, specially where the postmortem interval is prolonged and the value of other methods is limited. This field of study has unfortunately not received much attention in Indian Forensic Science Laboratories. This article highlights the different strategies of entomological studies including the brief history and the procedural guide.

Key words: Forensic Entomology, Postmortem interval, Procedural methods, Insect Evidence in Legal Investigation

Introduction

Corpses are attracted by various species of arthropods, primarily flies, beetles, mites, isopods opiliones, nematodes and their larvae. They feed, live and breed in and on the corpse, which depends upon their biological preferences and on the state of decomposition1,2. Their identity and stage of development can provide useful indicators for the time and place of death.

The importance of estimating the postmortem interval in a case of suspicious death cannot be overstressed. Several methods exist for this purpose that are based upon the changes occurring in a death body, collectively known as” postmortem changes”. These changes includes postmortem lividity, rigor mortis3, postmortem cooling4, changes in the chemical constituents of the body5, autolysis of the tissues and decomposition due to bacterial activity within the body. But these values that are based on postmortem changes are of little significance during the last stages of body decay. The putrefactive changes seen within few hours after death in summer may not be evident even after several days in winter at the same place. Under such circumstances it is believed that the study of arthropod forms infesting a corpse can reveal data more useful in calculating the time of death as claimed by many investigators6-10.

From a Forensic Science viewpoint the universality of the decay process provides two major advantages. Information based on the decomposition of animals is of considerable value when considering human cases and the successional pattern of decay is broadly equivalent wherever the process is being studied.

Literature on various aspects of forensic entomology is scattered between journals and publications covering entomology, ecology, insect’s physiology, forensic science, medicine and law. This dispersed literature has in the past provided the prospective students of the subject with considerable difficulties and has probably hindered the development of the science. Fortunately this situation has now been relieved by the publication of a bibliography of relevant papers in forensic entomology.

Historically, the usefulness of insects in solving crime can be traced back in the literature to the 13th century. The first documented forensic entomology case is reported by the Chinese lawyer and death investigator Sung Tzu in the medico-legal textbook “His yuan chi lu” (Translated by McKnight as “The washing away of wrongs”). He describes the case of a stabbing with sickle near the rice field in which the field workers were ordered to line up and lay their sickles on the ground. Flies began to be attracted to one of the sickles whereupon the owner confessed to the crime.

This article highlights the brief history of forensic entomology, Insects associated with carrion, postmortem dating, materials and methods of collecting insects and various factors affecting the forensic entomological studies.

Successional stages of decomposition

Decomposing bodies undergo biological, chemical and physical changes and at each stage of decomposition, they are invaded by a specific species of insect- often in a predictable sequence. Corpses pass through a series of identifiable but diffusely separated stages of decomposition. Table 1 depicts the various stages of decomposition along with the common found insects during each stage. (Table 1 to be attached here)

Insects associated with Carrion

Four ecological groups of insects are generally associated with carrion. They includes:

  1. Necrophagous Species
    • Important from forensic viewpoint
    • Most important carrion feeders
    • Includes blowflies (Sarcophaga and Calliphora) and Beetles (Dermestidae)

Table 1: Decomposition stage of corpse.

Decomposition Stages
At the moment of death—
breaking down of proteins and
carbohydrates molecule occurs during this stage.
Commonly found Insects
Adult Blowflies
Flesh Flies Ants
Inflate Corpse—Putrefaction starts Adult and larval blowflies
Carrion beetles
Deflate corpse—breaking of abdominal wall
and escape of gases from the body
Adult and larval blowflies
Carrion beetles Cockroaches
Post decay—byproducts of
decomposition found
Fungus beetles
Fruit flies
Dry remains BeetlesAnts

2. Predators

  • Are also important from forensic viewpoint
  • Feeds on other fly larvae
  • Example- Chrysomya

3. Omnivores

  • Feeds on both corpse and its inhabitants
  • Examples- Wasps and Ant

4. Adventives Species

  • Includes such species which uses corpse briefly as a resting or feeding site.
  • Example – Spiders etc.

From a forensic viewpoint, the most important orders of insects are the flies (Diptera) and the beetles (Coleoptera). Adult Diptera are also known as true flies. They have one pair of prominent wings. The second pair of wings is reduced and is used to stabilize flight. The blowflies (Diptera, Calliphoridae) are the first colonizers of carrion and hence are important in estimating the time of death. Beetles tend to colonize corpses later than the Diptera. They are uniform in structure and can be identified by their biting mouthparts and elytra. The black soldier fly (Stratiomyidae) infests corpses in advanced stages of decomposition. Thus a through knowledge of life cycle duration, age and stage of the insect occurring on the carrion along with data on other cohabiting arthropod species, under prevailing local environmental conditions, provides investigators with valuable data to form a template for dating the remains.

Post-Mortem Dating

Cases in which forensic entomologists are often involved are mostly 72hrs or more old. This is because until this time, other forensic methods are equally or more accurate than the insect evidence. After three days insect evidence is often the most accurate and sometimes the only method of determining elapsed time since death.

The two main ways by which insects can be used to determine elapsed time since death are:

  • Entomological succession: useful when the corpse has been dead for between a month up to a year or more.
  • Maggot’s age and development: useful when the corpse has been dead less than a month prior to discovery.

Forensic Entomology: A Procedural Guide

The first and most important stage of the procedure involved in forensic entomology involves careful and accurate collection of insect evidence at the crime scene. Insects should be collected from different areas of the body, from the clothing and from the crime scene. They often congregate in wounds and in and around natural orifices.

The two main insect groups on the corpse are:

  1. Flies (Diptera)
  2. Beetles (Coleoptera)

Diptera: can be found as

Eggs:

  • Very tiny in size and laid in clumps.
  • Usually found in wounds or natural orifices.
  • Collected either with paint brush dipped in water or with forceps.
  • Preserved either in 75% alcohol or 50% isopropyl alcohol.

Maggots

  • Found crawling on and near the remains.
  • Preserve specimen of each size by immersing them in hot water for few minutes and then putting them in 70% alcohol or 50% isopropyl alcohol.

Pupae and Empty Pupal Cases

  • Extremely important from forensic viewpoint.
  • Found in clothing, hair or soil, near the body hence often easy to miss.
  • Ranges from 2-20mm in length
  • With oval shape like a football.
  • No need to preserve pupal case, as they do not grow.

Adult flies

  • Useful only as an indicator of insect species.
  • Can be collected with net.

The presence of empty pupal cases indicates that an insect has developed on the corpse and reached adulthood. Beetles: can be found as

  • Adult, larval or grubs, pupae and also as cast skin.
  • Fast moving species and are often found under the body.
  • Preserve in vial with some air.

Insect collected from one part of the body should be kept separate from those from another area. Different species should be kept separate as beetle larvae feed on fly larvae.

Each vial should be labeled with:

  • Area of body / soil / crime scene
  • Date and time of collection
  • Development stage, as for example if larvae, it should be mentioned, so that if the specimen are pupae when received in laboratory, it can be said that they developed into the next stage during transit.

Limitation of Forensic Entomologist

Though Forensic entomologist can effectively establish the time of death, it has its own limitations. The temperature of the crime scene is very important factor and it rarely happens that the criminal is thoughtful enough to kill their victim right underneath the weather station. In most cases weather records come from station that are located at far distance from that of the crime scene. Hence it is necessary to determine the difference between the two sites. Secondly the microclimate of the corpse itself will be slightly different from its surrounding are, especially when the maggot mass is present. There it is important to know whether masses are present.

The results of forensic entomologist are not immediate. It takes time to rear the insects. Recently this time is reduced by the DNA technology, which speeds up the identification of immature species. Some time the dead bodies are disposed in such manner that it excludes insects. For example:

  • When the body is frozen for a period of time and then placed outside, the insects will only invade then, thus giving a misleading impression that the death has occurred recently. However the insect evidence in such cases will still determine the time of exposure.
  • When the dead body is buried deep, most insects will be excluded. However the criminal burials are not deep since their aim is merely to conceal the body. In such cases most insects will dig down to the body if there is blood soaked in soil. Hence insect’s evidence can still be used in such cases.
  • Presence of drug may affect the development of the insect, thus giving a wrong interpretation of time of death.
  • More research is needed for the insect successional study from different geographical region.

Conclusion

Forensic entomology is a very useful method of determining elapsed time since death after 72hrs. It is accurate to a day or less, or a range of days, and may be the only method available to determine elapsed time since death. It is vital that the insects are collected properly and its accuracy depends on this and on suitable conditions for insects. Insect succession varies from geographic region to region and the species and the time of colonization must be developed for all areas using this type of evidence. Unfortunately many laboratories in our country do not deal with this specific subject. Factors like insect activity, ambient temperature, rainfall; burial depth, presence of carnivores etc should be observed for the outcome of a successful investigation. Interest and growth in this field can be generated only when forensic entomology is introduced as a special paper in the academic curriculum of Post Graduate in Forensic Science.

Acknowledgements

Authors are thankful to DR M. P. Goutam, Director, State Forensic Science Laboratory, Raipur for his valuable suggestions.

References

  1. C. E Abbott, The necrophilous habit in Coleoptera, Bull. Brooklyn Entomol. Soc. 32, 202-204,1937.
  2. F. J. Illingworth, Insects attracted to carrion in southern, California Proc. Hawaiian Entomol. Soc. 6, 397-401,1926.
  3. R. S. Fisher, Time of death and changes after death, In W. U. Spitz and R. S. Fisher (eds.), Medico-legal Investigation of Death, 2nd edn., Charles C. Thomas, Illinois, USA, 1980.
  4. A. E. A. Joseph and E. Schickele, A general method for assessing factors controlling postmortem cooling. J. Forensic Sci.,15, 36-42, 1970.
  5. W. W. Jetter, Post-mortem biochemical changes, J. Forensic Sci., 4, 330-338, 1957.
  6. P. Nuorteva, Sarcosaprophagous insects as forensic indicators. In C. G. Tedeschi et al.(eds.), Forensic Medicine: A study in Trauma and Environmental Hazards, Vol. 2, Saunders and CO. , Philadelphia, London, Toronto, 1072- 1095, 1977.
  7. Y. Z. Erzinclioglu, The application of Entomology to Forensic Medicine. Med. Sci. Law, 23, 57-64, 1983.
  8. B. Keh, Scope and applications of Forensic Entomology. Annu. Rev. Entomol., 30, 135-154, 1985.
  9. C. Vincent, D. K. Mc.E Kevan, M. Leclerq and C. L. Meck, A bibliography of Forensic Entomology, J. Med. Entomol., 22, 212-219, 1985.
  10. K. G. V. Smith, A manual of forensic entomology, British Museum (Nat. Hist.) London 206, 1986.
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