Forensic Entomology is the scientific study of the invasion of the succession pattern of arthropods with their developmental stages of different species found in the decomposition cadavers during legal investigations.

It is the application and study of insect and other arthropod biology to a criminal matter.

In forensic entomology, we mainly study the forensic entomological evidence (flies). In forensic entomology, we study hexapod flies (the fly having six legs). 

Arthropoda

The largest phylum (i.e., the one with the greatest number of living species) of the kingdom of Animals is Arthropoda. To be called an Arthropoda, the organism must have the following characteristics: The typical adult insect has three body parts, six legs, two antennae, compound eyes, external mouthparts, and wings.

Exoskeleton

It is chitinous (made up of chitin), a non-living, waxy, moisture-proof which serves the purpose of protection and providing a place for muscle attachment.

• It is often hardened by the deposition of calcium or silica. The organism must shed its exoskeleton to grow as part of a process called moulting.
• The exoskeleton gives rise to many appendages and projections modified for protection, preduction, sperm injection, filtering food, sensing and communication, and much more.
• Segmented body the number of segments can vary in different arthropods.
• Antennae are the modified projection made up of chitin used for sensing the environment and for communication.
• Compound eyes are made up of specialized cells called ommatidia, which detect the stimulus of eyes and rarely form an image different from ours.
• The main body cavity is called coelom and possesses bilateral symmetry (i.e., the body can be cut into two mirror-image using one plane only).
• An open circulatory system consists of a tubular heart, blood-like fluid (hemolymph) with no red blood cells, and haemoglobin. Most arthropods don’t need to transport oxygen, but some have a blue-pigment protein, called hemocyanin dissolved in their hemolymph.

Tagmosis has produced the three functional body segments of insects: the head, thorax, and abdomen

• The Head is where the feeding, appendages are located and also has sensory inputs.
• Thorax is a body part associated with locomotion. Most adult insects have six legs. There are exceptions in certain groups of insect files.
• The abdomen is the location for the majority of the organs involved with digestion, excretion and reproduction.

Sensory Organs

Insects perceive their environment in a similar way to humans, but with a different emphasis.

Smell is the most important sense to identify the source of food. The primary structure involved with the sense of smell is the single pair of antennae which extend from the head and are extremely sensitive to identifying the various smells.

In forensic entomology, we mainly study the Calliphoridae family, the Sarcophagidae family, and Bettles.

Calliphoridae (commonly known as blow flies, carrion flies, bluebottles, greenbottles, or cluster flies) are a family of insects in the order Diptera, with almost 1,900 known species.

Blowflies are usually the first insect to come in contact with carrion because they have the ability to smell dead animal matter from up to 2km (1 mile) away.

Upon reaching the carrion, females deposit eggs on it. Blowflies give the expulsion of eggs from the oviduct to the external environment and this process is called as oviposition. Since the developmental stages of these insects are known, blowflies are considered a valuable tool in forensic science.

Sarcophagidae is a family of flies commonly known as flesh flies.

Flesh flies are the insect that comes after the blow flies. After the entery of flesh flies, they start to eat the flesh and the maggots (eggs) of the blow flies.

Flesh flies never give eggs they directly lay larvas and this is called larviposition (larviposition- the expulsion of the larva by the adult flies to the external environment).

Lief Cycle of Flies

Adult flies (Blowflies) are the first insect which arrives at the cadaver and starts to take a nutritive thing and lay maggots at the natural opening of the body (eye, ears, nose, mouth, abdomen)of the remains.

After the oviposition, it gets converted into larvae (first instar) in 23 hours.

After this larva starts to get mature by taking the nutritive substance and converting into the second instar in 27 hours, and then the third instar in 22 hours.

For the formation of pupae, it takes 130 hours and then pupa is converted into an adult fly in 143 hours, at 70 degrees Fahrenheit (21.111 degrees Celsius) each stage of blowfly life takes a known amount of time to complete.

If the temperature is more than 70 degrees Fahrenheit the process gets slow and the size of the pupa gets smaller and  because of the temperature, the flies get to die in that pupa.

Beetles are the insects from the order Coleoptera. They arrive at the cadaver after the blowflies and flesh flies, beetles are the insect which helps in the process of decomposition. This organism fed on carrion.

Decomposition of Human and other vertebrates remain is a complex process

• The moment that a human or any other animal dies, immediate change begins to occur that start the process of decomposition.
• Taphonomy is the study of decomposing or decaying organisms over time, including the processes leading to fossilized remains.
• Features of the environment such as temperature, moisture levels, whether the body is found in a terrestrial versus aquatic environment, geographic location, and if vertebrate scavengers and insects have access to the corps can all change the rate of body decomposition as well as other aspects of tissue decay.
• Chemical decomposition is more narrowly classified into two categories: autolysis(self-digestion or destruction of cells due to the action of enzymes) and putrefaction(chemical decomposition of soft tissues).
• The breakdown of cells and tissues is dependent on both abiotic and biotic decomposition.
• With the help of conspecifics(Belonging to the same species but different stages) and allospecific (belonging to different species) the rate of decomposition and reproduction get high.

Estimate of Time Since Death

Forensic entomology is a specialised area of investigation; reference to guidance notes on the collection and preservation of specimens is essential. Incorrect storage, e.g. immersion of live maggots in ethanol, may lead to errors in the estimation of larval age based on size.

Although blowfly larvae are the most important specimens for use in forensic entomology, another insect should also be collected, particularly if the cadaver is more than 10 days old.

Maggots are commonly found in and around the body orifices, in wounds, on the skin of the head, between the foreleg and chest(axilla), over the abdomen and on snares encircling the neck.

Maggots also invade the body and may be found in the windpipe, gullet and body cavities. By collecting the forensic entomological evidence we can find the time of death.

Conclusion

Forensic entomology is a new innovative tool for solving criminal activities because in recent times crime increased day by day like muders, and suicide so in those conditions forensic entomology tries to estimate the time of death and place of crime and many other legal issues.

PMI is one of the important aspects in crime detaction and with the help of insects PMI can be calculated very easily.

PMI can be estimated only within first 72 hours of death by observing eggs, 1st , 2nd , 3rd instar larvae, pupa and adult flies.

The correct sampling and proper interpretation of the visiting insects on carrion can provide valuable information in forensic investigations. 

Written by: Tisha Ramteke