Forensic Entomology: The Use Of Insects In Criminal Investigations

Forensic Entomology is a sub-field of forensic biology. It applies the knowledge of the field of entomology to identify, collect, and study the type of insects found in close proximity of the cadaver in solving cases of crimes. Nowadays, it has become an important branch of forensic science.

Forensic Entomology: The Use Of Insects In Criminal Investigations

Entomology is the scientific study of insects. It is a branch of zoology. It deals with the study of the insects at the taxonomic, ecological, morphological, paleontological, biochemical, genetic, and behavioural dynamics

In this, the biology and ecology of insects are studied to determine the time since death or post-mortem interval. It involves the study of insects such as arthropods, centipedes, arachnids, millipedes, and crustaceans to criminal or medico-legal cases. 

The insects and their various developing stages such as egg, larvae, pupa, and adult insects are collected to correlate their life cycle with the stages of decomposition of the dead body. The new branch of entomology that is entomo-toxicology is useful in detecting the drugs and poison from the insects and their developing stages and relating them with the fact that the carcass was intoxicated before death.

Why Use Insects in Criminal Investigation?

The insects are expected to live for 250 million years. Till now the insects have attained the diversity in both forms and behaviour due to their hard exoskeleton, capacity to survive in a wide range of the environment, and high rate of reproduction.

The insect evidence is useful if the information they provide is appropriately collected and interpreted. Insects can help in understanding what happened in a criminal event because they can be found everywhere. On land as well as in freshwater, the insects are the most abundant organisms.

According to the experts of the American Board of Forensic Entomology, the insects help to discover the site where the crime was committed. They can throw up light involving crimes like smuggling of drugs.

A Brief History Of Forensic Entomology

Bergeret d’ Arboris (1814-1893): He was a physician in a French Hospital. He was the first who related the entomological evidence to solve a crime. He published a report in which he stated the life cycle of insects and made many assumptions about the mating habits of these insects.

Hermann Reinhard (1881): He was a German medical doctor who played a vital role in forensic entomology. He used the exhumed bodies to study the development of various insect species. He concluded and identified some insect species which feed over the carcass.

Jean P. Megnin (1828-1905): He published many books and articles which are important for describing forensic entomology. He studied the larval and adult forms of insect families found on the cadavers. He developed the research work describing a relationship between the deceased and arthropods.

K. Tullies and M. L. Goff (1994): Described the relationship of five stages of decomposition of a human carcass and their association with the feeding insects population on it.

Application Of Forensic Entomology

  • Pest Infestation Investigation

An investigation based on cases of pest infestation in mills, buildings, gardens, agriculture fields, gardens, parties, and their associated toxicity and deaths can be encountered by forensic entomology. The pesticide toxicity can be detected in the case of the use of pesticides in the agriculture field, garden, food storage rooms, and others.

  • Medico-Legal Investigation

This involves the searching, identification, and collection of entomological evidence from the scene of the crime like murder, rape, physical abuse, suicide, and contraband trafficking. The study of insects associated with the deceased or near the dead remains can help in establishing the following:

  • The Time Since Death or Post-Mortem Interval

With the age of the carcass after death, the diversity and complexity of the insects feeding over its increase, which helps in establishing the time since death. The life cycle of insects can indicate the time since death.

  • The Place of Death

This can be determined by careful examination of insects found associated with the dead carcass remains. As the insects where the crime took place can be different from those where the carcass was found.

This is an important scientific study that can state the fact that the rate of decomposition is accelerated or not after death. Also, it can help in establishing the fact that what was position of the body after death indoor or outdoor. In the case of indoor death or crime, there will be very few species that can be found on the deceased whereas, in the case of outdoor death or crime, many insect species can be found.

  • Entomo-Toxicology

It involves the analytical study of insect samples collected from the crime scene or in close proximity of the carcass or dead remains. This can help in establishing the fact that the body was under the influence of drugs or poison before death or drug or poison were the cause of death. It is a new branch of entomology.

However, the extraction and identification of the drug or poison from the body of the insect is not an accurate indicator of the substance that was responsible for toxicity. As the toxin which is being taken by the insect from the dead body does not exist in its original metabolic form. Also, the substance can disturb the developmental stages of the given insects.

 

That is the substance can accelerate, slow down, or stop the development of the insect colonies. This can give false results for the life cycle growing over the carcass and incorrect determination of the time since death, place of death, and other important relative information of the carcass with the insect growth.

An example of the entomo-toxicology was observed in which a 22 year old female found in bad decomposition condition. Phenobarbital drug was detected through the insects growing on the deceased.

Role Of A Forensic Entomologist

A forensic entomologist has to perform the following activities for the purpose of a criminal investigation.

  • Required to visit the scene of the crime, where he/she has to identify the human remains and insects, collects and preserves this evidence, and send them for laboratory analysis.
  • Studies various aspects of the insects, observing the type of insect, growth, development, and damage caused by these insects to the post-mortem body.
  • Determines whether the insect species is native to the place where the dead human or animal remains were found.
  • Required to prepare the expert testimony on the basis of the analysis of the insect evidence.
  • Presents the testimony in the court of law to provide the evidence for proving the commission of a crime.

Generalized Life Cycle Of Insects On Carcass

  • Egg Stage: The eggs are usually present in clumps over the natural orifices, and injuries. The eggs from laying to hatching take one day.
  • Larva First Instar Stage: The larva initially feeds over the fluids released from the decomposed body. The larva migrates over the body and remains for one day. The size of the larva in this stage is 2 mm long.
  • Larva Second Instar Stage: The larva moves over the body, and increases in size. The size of the larva in this stage is 5 mm long.
  • Larva Third Instar Stage: The larva moves in masses and greatly increases in size. This development takes two days. It is the main feeding stage. The size of the larva in this stage is 30 mm-50 mm.
  • Pre-Pupa Stage: The larva does not feed. It transforms into a pupa. This transformation takes four days.
  • Pupa Stage: It is the transitional stage from the larval body to adult insects. It does not feed over the body. This transformation takes ten days to complete.
  • Adult Insect: The adult insect feed over the body fluids, which contains the proteins essentially. These insects lay eggs over the carcass. The emergence of new insects from the pupa and finally laying eggs takes two days.

Types Of Insect Species Found On The Carcass

The time and type of insects that feed over the carcass vary considerably.

  • Necrophages Species: These species are attracted to the dead body initially. These start feeding on it and start their life cycle on it. Thus their presence accelerates the process of decomposition.
  • Predator Or Parasitic Species: These species feeds over the insects which feed over the body. In other words, these insect species are dependent upon the necrophagous species for their food requirements. Initially, these insects feed over the body, but later they start feeding on the insects already feeding over the body.
  • Omnivorous Species: These species of insects are not attracted by the dead body but also attracted by the insects present on it. Due to these insects, the establishment of time since death will become difficult. These insects interfere with the life cycle of other insects.
  • Incidentals: These are big insects such as spiders, mites, centipedes, and others. They find the dead body as a habitat. These are considered to be commonly associated with the dead body

Commonly Found Insects On The Carcass

The insects commonly found on the dead body and considered suitable for forensic investigation belong to Diptera. The related species are of the order-

  • Calliphoridae: These are the blowflies. These are the first species to arrive on the dead body. Their bodies are shiny with metallic coloring. These have blue or black abdomen.
  • Sacrophagidae: These are the flesh flies. These also arrive first on the dead body for feeding. These are medium-sized flies. They have grey and black stripes on their abdomen that run longitudinally over the body.
  • Muscidae: These are the house flies. These are 8 mm -12 mm in length, grey in color and they have four longitudinal dark lines on their back. They have a body with hair-like projections.
  • Piophilidae: These are the cheese flies. These are the small flies with a 4 mm length. These are used by forensic scientists to identify the date of death of human remains. These flies do not take residence over the corpse until three to six months after death. The adult fly color is blue-black, black, bronze, yellow on the head, legs, and antenna.

 

Some Other Insects To Study Under Forensic Entomology

  • Beetles: The beetles of the order Coleoptera are generally found on the dead body when it is in the decomposition stage. Some types of beetles associated with the decomposition stage are as follows:
      • Rove beetles: These are of the family Staphylinidae. These are elongated beetles that have large jaws. Their larval development is fast. Some adults are the early visitors to the corpse. They lay their eggs on the corpse. The larvae are also predators. They sustain themselves for long over the corpse.
      • Hister beetles: These are of the family Histeridae. The adults are the shiny beetles. These are metallic green or black in color. The main characteristic of these beetles is that they only remain active at night. During the daylight, they hide inside the dead body.
      • Carrion beetles: These belong to the family of Silphidae. The adult is of the size of about 12mm. These are called burying beetles as they feed upon the buried carcass.
      • Hide beetles: These belong to the family of Dermestidae. These can be found over the last decomposition stages of the dead body. The larvae and adults feed over the dried skin and bones. These beetles release enzymes which are responsible for breaking down the keratin protein present in the hair.
      • Scarab beetles: These belong to the family of Scarabaeidae. These beetles are heavy-bodied and oval in shape. They are clump together to feed. These species are known to be the heaviest insect species of the world.
      • Mites: Many mites feed over the early stages of decomposition like Macrocheles mites. While some of them also feed over later stages of decomposition like Tyroglyphidae and Orbatidae which feed on the dry skin.
      • Moths: These belong to the order Lepidoptera and the family Tineidae. These are closely related to the butterflies. These feed on the hair typically on the larval stage.
      • Wasps, And Bees: Some of them feed over the body, but some also feed over the insects on the body. The bees and wasps can be seen feeding during the early stages of decomposition. They may cause problems for the investigation of cases as they feed on the larvae and eggs of other insects. Thus will pose difficulty in estimation of time since death or post mortem interval before the crime scene investigators arrive at the scene of the crime.

 

Entomological Association With The Post-Mortem Changes

The body will decay over time in well-defined stages, and these stages are associated with the insect activities which are of various types.

K. Tullies and M. L. Goff (1994)

K Tullies and M.L. Goff have described the decomposition of the body in association with the insect colonies into five stages on the basis of the physical appearance of the dead body, and internal temperature.

The five stages are:

  • Fresh Stage: This stage remains for 1-2 days, and it is the initial stage of decomposition. In this, cellular destruction takes place. Insects are seen attracted to the dead body. In this stage, no oviposition takes place that is no egg-laying was found during the stage.
  • Bloated Stage: The tenure of this stage is 2-7 days. The putrefaction takes place at this stage. Gases accumulate in the body parts giving a bloated stage to the body. In this stage, a large number of Diptera insects can be seen on the dead body. The oviposition also occurs in this stage which is followed by first and second instar stages develop at the end of the four days.
  • Decay Stage: The tenure of this stage is 5-13 days. The walls of the abdomen get penetrated due to gaseous release. Decaying of the body takes place. This is also associated with the decrease in the weight of the body after ten days. The larvae transform into the pupate stage.
  • Post-Decay Stage: The duration of this stage is 10-23 days. It begins with the Dipteral larval stage which feeds over the leftover bones, cartilages, hair, and small portions of tissues.
  • Remain Stage: The duration of this stage is 18-90 days. It begins in the 18th day over the dried bones and over other skeletal remains. This is the last stage of decomposition. This is associated with a decrease in the population of insects.

Factors That Affect The Time Since Death

  • Physical factors

A body that is covered by a vault or a casket will be more resistant by the attacks of the insects than the one which is dumped into the hole. In the dark, it will be difficult for the insect to find the body and colonize over it then in full or partial light.
If the body is submerged in water or trapped in a car, the colonization of insects will be less than the body fully exposed to the external environment.

  • Chemical factors

Embalming chemicals also affect insect attacks on dead bodies. These chemicals are generally poison for some arthropods, so their activity will be greatly retarded by the presence of the embalming fluids. The drugs will also affect the activity of these insects. For example, stimulants such as cocaine will accelerate the activity of insects hence, accelerate the rate of decomposition, whereas the depressants can retard their activity. 

  • Climate

The high temperature will accelerate insect activity. The cold temperature and weather conditions will retard the activity of insects. This is due to the fact that in cold-blooded insects the rate of development is dependent upon the ambient temperature.

Bodies exposed to a large amount of sunlight will heat up easily that gives the insect a warmer area to develop, thus reducing the development time of the insect colony.

The damp weather enhances the rate of reproduction and growth in many insect types.
The high wind currents will cover and uncover the body with debris and will make it difficult for the insects to find and land over the body.

Read More- Environmental Toxicology- Study of Toxicants present In the Atmosphere

The hanged body is expected to be more varieties of insects than the landed bodies. As the hanged body is more exposed to the air and then drys out faster, which leaves fewer insects after some time. Heavy rains will wash off insects from the body, and if the body is partially submerged, the water can affect the insect activity.

  • Animals

Larger animals such as dogs, cats, rodents, and scavengers will attack and feed on the dead carcass. The body parts will be separated and eaten up by these animals. The leftover parts will become the target of these insects.

This will lead to an increase in the rate of decomposition, but little evidence and remains will be left at the scene of the crime which will pose difficulty in the identification of the unknown dead body and the cause of death.

 

Also, in the indoor crime scene when the victim is left with the pet, the pet is likely to consume the body due to hunger issues also may pose difficulty for determination of the cause of death.

Collection, Preservation, And Packaging Of The Entomological Evidence

  • To use entomological evidence for the purpose of utilization of this evidence in the court of law for the conviction of the criminals, collection without contamination is necessary.
  • While approaching the scene of a crime where insect evidence can be found, it is required to analyze the surrounding conditions.
  • If the scene of the crime is outdoor, then various aspects such as the position of the body, condition of the floor, soil type, weather condition, type of vegetation should also be recorded.
  • Also, the temperature is an important factor in the case of the outdoor crime scene. The increase in temperature will give rise to the increase in the diversity of insect species.
  • In the case of the indoor scene of the crime, the crime scene investigator should search upon the orifices or the ways through which the insects can enter the indoor and affect the body.
    The soil sample should also be taken as evidence.
  • The samples of entomological evidence should be collected with a soft brush and must be collected in alcohol or boiled water in a glass sealed container. This step will stop the development of the insect and will allow the investigator to identify the stage of development in which the insect was growing so that the time since death can be identified with the developing stage of the insect.
  • The flies can be collected by using wire nets.
  • Eggs are usually present over the natural orifices and sites of injuries. These are usually found in clumps. These should be collected for the identification of species and are useful when later stages of insects are not available.

Techniques Used In Forensic Entomological Investigation

  • Scanning Electron Microscopy

The insect larvae, eggs, and other minute body parts can be examined, observed, and identified using scanning electron microscopy can be useful in the determination of the post-mortem interval of time since death. This technique can provide information about different morphological features of the insect life cycle.

  • Potassium Permanganate Staining

It is a low-cost technique. This 1% potassium permanganate solution is used along with the normal saline. The collected entomological evidence is rinsed in the solution. The samples are observed under a light microscope.

The features like identification of the stage of the life cycle of the insect, shape, size, length, and width of the stages can be determined by this method. All these features contribute to the determination of the species of insects and time since death.

  • DNA Profiling

The DNA profiling of the insect samples can be useful in the determination of the species. This process can help in determining the time since death as well as the place of death. As the more complex the insect form, the more time has passed since death also different regions of the world are associated with the diversity of different insects common to a particular place or location.

Educational Requirement To Become A Forensic Entomologist

A forensic entomologist is a scientist who is qualified in the specialized field of entomology. At bachelors level must have studied biology or chemistry course. A forensic entomologist is a Ph.D. degree holder in the field of forensic entomology or a master degree holder of forensic science with a specialization in forensic entomology.

Moreover, experience in the field, as well as laboratory analysis, is required to become a forensic entomologist. Thorough knowledge and skill of collection, handling, and packaging of the entomological evidence are required.

Forensic entomologists are placed in local as well as state government forensic laboratories. They can also gain placement in medical and diagnostic laboratories and in universities as a lecturer of forensic entomology.

Limitations Of Forensic Entomology

  • The field of forensic entomology suffers from many limitations. For example, there is no set pattern of insects that grow in particular conditions such as in moist soil, dry soil, humus-rich soil, in different seasons and places.
  • On the collection of entomological evidence, mixed patterns of insect species are collected out of which many of them are unknown.
  • There is no well-developed classification system and digital database which can be referred to while identifying the insects in relation to their life cycle, climate, soil type, condition of the body such as infection, toxicity, injury, etc.
  • The growth of the insects growing over the carcass will vary depending upon the substance (drug or poison) they have ingested from the dead body. This can mislead the findings of the case.
  • Insects can enlarge or distort the bullet or knife or any other type of injury which can mislead the investigation.
  • They can disturb the blood spatter, or they can form pseudo blood spatter by transferring blood by the insects or larvae to another surface.
  • The use of insects and their life cycle is new in a criminal investigation. It began in the 19th century but still, it is known by very few people, involving the police officers who even don’t know this science(forensic entomology) really exists and useful for the investigation.
  • The rate of development of insects and fauna of insects can vary from country to country and even from place to place within the same country. Also, with the change in topology and climate conditions, this will be incorrect to refer to the entomological data of one country for solving the medico-legal case of other countries.

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