All through our lives, we think that our body is precious. But is it really true?

Actually, a living body is valuable until it has life. Without life, this “living machine” is considered dead.

So, does it mean that the human body is of no use?

The answer to this is obviously no.

The human body attracts life not only when it is living but also when it is dead.

Dead bodies or corpses are the breeding grounds for insects, the largest class in phylum Arthropoda, where they dine in until they convert the dead bodies into skeletons.

This group of invertebrates is a treasure for both, the crime scene investigator and the host which they are feeding upon.

These bugs on bodies act as a witness to death of a person ans help the investigator in estimating the Post Mortem Interval (PMI) commonly termed as ‘time since death’.

The possible location of the deceased can also be determined by linking the species of insects recovered from the corpse with the crime scene. These findings may prove significant in crime scene investigation and help provide justice to the victims.

The study of these insects, their developmental biology, and their application to legal matters is covered under a separate domain of forensic science which is termed Forensic Entomology.

The field of forensic entomology is considered as one of the incredible areas of investigation in all those cases which involve the determination of “Post mortem interval” as it provides all relevant information regarding the type of case, place of crime, nature of the crime, time of crime and mode of death.

To estimate time since death one may consider different parameters like a drop in body temperature after death, and physical (morphological) changes (like post mortem lividity) and biochemical post mortem changes such as the onset of rigor mortis, algor mortis, etc. but such procedures are very crude in nature and are not found to be a consistent method for doing the same, making this branch of forensic science imperative in estimating time since death.

What Attracts Insects to Human Cadavers?

Corpse faunae are considered remarkable forensic indicators due to their ability to get attracted towards human cadavers. But what makes these insects come near and around the dead body is something that left researchers to ponder on.

As death comes, individual cell of the person starts dying, releasing the digestive enzymes into the extracellular fluid and the microbes present in the gastrointestinal tract eat up the soft tissues, producing liquids and gases like hydrogen sulfide, sulfur dioxide, methane, ammonia, hydrogen, etc. which attract the insects to the corpse and induce behavioral changes in them.

Studies have shown that sulfur-based compounds are responsible for attracting insects whereas ammonia-rich compounds induce oviposition in flies.

Insects follow a definite pattern of successive life stages which is affected by the ambient conditions and the conditions of the carrion on which they are colonizing. This enables the investigator and the pathologist to ascertain the time since death.

Corpse Fauna

Species richness is another factor that helps the investigator in linking the dead body with the scene of the crime. Not all species of insects can be found on corpses each and every time at a scene of the crime.

Owing to the habitat variation, insects and their arthropod relatives differ in their life span which makes them imperative in the field of forensic science.

Various insect species ranging from necrophagous to omnivorous feed on the decomposing body. Species from the order Diptera and Coleoptera are the most prominent ones encountered by forensic entomologists.

Order Diptera covers true flies such as insects from the species Calliphoridae (blowflies), Sacrophagidae (flesh flies), and Muscidae (house flies); blowflies and flesh flies colonize the carrion immediately after death. Species in Order Coleoptera include beetles which come and colonize during the later stages of decomposition.

The forensic entomologist must be well versed with the information about successional waves of insects and maggot age and development in order to proceed with the investigation in such types of cases. 

The knowledge regarding these parameters of forensic insects assists in ascertaining the time since death. 

The body encompasses several stages of decomposition which usually overlap with the type of insect attracted by it. By studying these insect assemblages in parallel to decomposition stages, the investigator could formulate a time frame in which death took place.

A general understanding of insect type on dead bodies suggests that blowflies and fleshflies are the first witnesses to death. In addition, there exist certain insect species that are aphidophagous in their feeding habits.

These flies first feed on carcasses and then transform into predators for other insect species.

Also, certain flies are seasonal and thus their colonization can be associated with the season during which a dead body is retrieved from the scene of the crime. This transition from one insect assemblage to the other is extremely helpful in ascertaining PMI.

Insects follow a set pattern of larval stages within a predefined time frame.

The study of maggots or the successive stages of development of these immature eggs is considered useful in estimating time since death.

The flies are oviposited inside the wounds or the natural orifices and eggs are hatched into first instar larvae which then feed on the decomposing cadaver and are molted into second and third instar larvae respectively. 

This cycle is predictable and thus helpful in determining the date of death by studying the whole process of maggots deposition till their development into an adult fly retrospectively.

The limitation to this method is that it is useful until the first adult generation is developed, after that estimation of the time during which death took place can be done using different insect assemblages arriving at the dead body at different times.

Conclusion

Bugs on bodies undoubtedly offer a huge advantage to forensic investigators and pathologists by providing answers to the question of paramount importance (i.e. estimation of time since death) that stirs up their minds from the very beginning of the investigation and can be considered as credible witnesses to death.

But the information that entomological evidence provides is limited to only one aspect of the investigation process i.e. the time and place of death to some extent.

This evidence, along with all other evidence and clues, helps the investigator in solving criminal conduct related to death. Thus, whenever there is a need for determining time since death the field of forensic entomology must not be forgotten.