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Decomposition & Insects - How Relevant in Forensics?

Authored by - Ruma Minj

Keywords - Forensic, Decomposition, Insects, Arthropods, Death, Forensic Entomology, Larvae, Post mortem.


Forensic is an indispensable part of criminal cases. It plays a significant role as it provides answers about deceased individuals to assist court procedures, particularly those which are related to the cause of death and identification of unknown victims.


Decomposition is the natural process through which large organic materials and molecules are broken down into simpler ones. Living organisms are basically comprised of cells and tissues which are made up of complex organic molecules that enable the organisms to maintain and add macromolecules necessary for existence. However, after demise, such maintenance and growth functions cease. Therefore, after the death of the living organisms decomposition procedure commences. It begins to break down the cells that are their component molecules and macromolecules into simpler organic and inorganic molecules.


Insects are also a very indispensable part of forensic sciences. The study of insects or arthropods associated with the crimes and other aspects of the courts and judicial system are called forensic entomology. Forensic entomology basically pertains to the identification of insects and other arthropods associated with human remains as an aid in order to determine the time and place of death.


Decomposition research in forensic anthropology especially concentrates on estimating the postmortem interval, detecting clandestine remains, and interpreting the context of the crime scene. The cycle of decomposition is generally classified into five stages on the basis of the physical appearance of carcasses, internal temperatures, and characteristic insect populations:

1. Fresh Stage: This is the first stage that occurs between 1st and the 2nd day. It begins at the moment of death and when the bloating of the carcass is observed. Autolysis occurs at this stage. The estimation of the time of death by entomological data after 24 hours is more accurate than the medical examiner's estimation based on the soft tissue examination. Insects get attracted within the initial 10 min of death to the carcass but no egg laying is found during this stage. The cellular breakdown is observed during this stage without morphologic alterations. Although morphological changes and odors are not obvious to humans, the chemicals released from the cellular breakdown attracts insects even in this early stage.

2. Bloated Stage: This is the second stage which is observed between the 2nd to 7th day. Putrefaction commences at this stage. Gases produced by the metabolic activities of anaerobic bacteria cause inflation of the abdomen and the carcass forms a balloon-like appearance during the later part. Arthropod activities combined with the putrefaction processes cause internal temperatures of the carcass to increase. During this stage, the greatest number of adult dipteral larval gets attracted to the carcasses.

3. Decay Stage: This is the third stage which can be witnessed during the 5th to 13th day. The abdominal wall is penetrated, resulting in the deflation of the carcass and ending the bloated stage, the internal temperature increases to 14 degrees and above the ambient temperature followed by a drop which symbolizing the end of the decay stage. Decaying odors are high during increased temperatures and drop with the decline in temperature. There is a steady reduction in the weight of the carcass by the 10th day.

4. Post-decay Stage: This is the fourth stage which takes place from the 10th to 23rd day. The post-decay stage starts when most of the dipteral larvae leave the carcass leaving behind bones, cartilage, hair, small portions of tissue, and a large amount of wet, viscous material known as byproducts of decay.

5. Remains Stage: This is the fifth and last stage which is observed from the 18th to 90th day or after that. This stage is mainly characterized by bones with little cartilage remaining and the byproducts of decay have dried up. The transition from post-decay to remains stage is gradual, with declining adult and dipteral larval populations.


Insects and their actions serve as very crucial evidence within the legal system. Medico criminal entomology includes insects as a piece of evidence in criminal cases and mostly in homicide cases which are associated with the term forensic entomology. The usage of insects in order to estimate the postmortem interval needs an understanding of the insect's life cycle, the relationship of the insect to the remains, and the relationship of the remains to the habitat in which they are found.

Insect evidence can be helpful in case the information is appropriately collected. Careful observation with knowledgeable expertise at a crime scene can lead the investigator to interpret how long the victim has been in contact with the insect activity. Insects help to understand what happened in the criminal case because they are found everywhere.

Role of Insects in Decomposition

The analysis of the insect present on a decomposing corpse can provide valuable forensic insights, especially the estimation of the time of death or postmortem interval. The life cycle of insect act as precise clocks which commences instantly after a few minutes or hours after death. When other methods are not able to provide reasonable information than the life cycle of insects holds immense importance in postmortem interval estimation.

Time of Death

The time of death can also be ascertained based on the ambient temperature and other weather conditions over the preceding days at the crime area and by associating this information with the developmental rates of arthropod species or insects existing in the corpse. These arthropods are generally fly larvae, some of which are important primary and secondary decomposers. After knowing the developmental times and related information for decomposer species at various temperatures, it is possible to accurately estimate the time of death.


The location where the crime took place can also be specified by the presence of insects. In case the place of crime is distinct from the area, where the body was found then it can be determined through the presence of unique insects and arthropods. Similarly, a thorough examination of collected insect evidence can also aid in solving other crimes such as the origin of drug shipments and sources of vehicles and other accessories used in crimes in which there is arthropod evidence.


Forensic entomology is a developing field in forensic sciences where the insects which are present on corpses are studied. It has now become an important tool in criminal investigations. From the very early stage insects get attracted to the decomposing body and lay eggs in it. Through the study of insect population and the developing larval stages present in dead body forensic scientists can estimate the postmortem index, any change in position of the corpse as well as the cause of death.





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