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:
- 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:
- Flies (Diptera)
- 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
- C. E Abbott, The necrophilous habit in Coleoptera, Bull.
Brooklyn Entomol. Soc. 32, 202-204,1937.
- F. J. Illingworth, Insects attracted to carrion in southern,
California Proc. Hawaiian Entomol. Soc. 6, 397-401,1926.
- 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.
- A. E. A. Joseph and E. Schickele, A general method for
assessing factors controlling postmortem cooling. J.
Forensic Sci.,15, 36-42, 1970.
- W. W. Jetter, Post-mortem biochemical changes, J.
Forensic Sci., 4, 330-338, 1957.
- 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.
- Y. Z. Erzinclioglu, The application of Entomology to
Forensic Medicine. Med. Sci. Law, 23, 57-64, 1983.
- B. Keh, Scope and applications of Forensic Entomology.
Annu. Rev. Entomol., 30, 135-154, 1985.
- 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.
- K. G. V. Smith, A manual of forensic entomology,
British Museum (Nat. Hist.) London 206, 1986.
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:
- 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:
- Flies (Diptera)
- 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
- C. E Abbott, The necrophilous habit in Coleoptera, Bull. Brooklyn Entomol. Soc. 32, 202-204,1937.
- F. J. Illingworth, Insects attracted to carrion in southern, California Proc. Hawaiian Entomol. Soc. 6, 397-401,1926.
- 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.
- A. E. A. Joseph and E. Schickele, A general method for assessing factors controlling postmortem cooling. J. Forensic Sci.,15, 36-42, 1970.
- W. W. Jetter, Post-mortem biochemical changes, J. Forensic Sci., 4, 330-338, 1957.
- 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.
- Y. Z. Erzinclioglu, The application of Entomology to Forensic Medicine. Med. Sci. Law, 23, 57-64, 1983.
- B. Keh, Scope and applications of Forensic Entomology. Annu. Rev. Entomol., 30, 135-154, 1985.
- 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.
- K. G. V. Smith, A manual of forensic entomology, British Museum (Nat. Hist.) London 206, 1986.
