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Forensic Science (Entomology): Secrets Revealed by Flies and Bugs

Updated on June 16, 2018
Schatzie Speaks profile image

Schatzie has two bachelor's degrees, one in science and the other in English. She is working on her master's degree.


What is Forensic Entomology?

Different bugs are present on a corpse during each stage of its decomposition. Using facts known about these insects, information can be learned about the body they infest.

General details are provided here on the five levels of corpse decay: fresh, bloated, active, advanced, and dry. A discussion follows on how the bugs present in each of these contribute to criminal investigations.

______________The Five Stages of Decay______________

Stage of Decay 
Bugs Present 
the blow fly 
the blow fly, flesh flies, house, latrine & dump flies 
blow flies, flesh flies, house, latrine & dump flies, rove beetles, carrion beetles 
rove beetles, carrion beetles, histor beetles, black scavenger flies, small dung flies, dung flies, soldier flies, scuttle flies 
skipper flies, checkered beetles, sap beetles, larder&carpet beetles, hide beetles, pyralid moths, clothes moths 

The Blow Fly: Present in Fresh through Active Decay

The blow fly usually lands upon a corpse within minutes.

The female flies locate moist areas in which they lay their eggs. After hatching, larvae undergo three stages of development, lasting a combined total of 7 to 10 days. At this point they leave the corpse, seeking drier areas where they develop into pupae. Pupae later split open to release adult blow flies, signaling the completion of the final stage of growth.


Flesh, House, Latrine & Dump Flies: Present in Bloated through Active Decay

Flesh, House, latrine & dump flies appear within the first days of death to feast on the corpse's bodily secretions. Flesh flies lay live larvae upon a body; the others deposit eggs. All maggots go through three developmental stages. Life cycles last for approximately two weeks.


Rove, Histor and Carrion Beetles: Present in Active through Advanced Decay

Rove, Hister, and Carrion beetles and other insects such as ants, wasps, spiders, and mites show up after the eggs of blow flies hatch and actively feast upon the emerging larvae as well as each other. They remain on a corpse as long as it retains moisture.


Moths: Present in Dry Decay

Once fully dried, Pyralid and Clothes Moths find and reproduce within whatever is left remaining of the body.

Bugs Verify the Scene of the Crime

A body and the bugs infestating it must be directly linked to the believed scene of a crime. It must be explained why each insect was present and whether or not it should have been, considering where the body was found. If there are inconsistencies, the body may have been moved.


Bugs Determine Time of Death

The precision with which time of death can be estimated is highest when bodies are found within one month. If found at a later time accuracy suffers. Of the relevant insects, blow flies are the most commonly used for calculations.

The Importance of the Blowfly

These flies generally arrive almost immediately upon death. Because they lay eggs soon after, if it can be determined what time eggs were laid, it can be determined when a person died.

For this reason, the life cycle of the blow fly has been well studied and the length of each of its main developmental stages has been scientifically determined. Based on the stage larvae are found on a body, scientists can backtrack through their previous stages of development and find the time elapsed since they first hatched. This calculation is key in determining the approximate time of death.


The Use of Other Bugs

When bodies are found in later stages of decay, they lose moisture and no longer contain blow flies. In this case other insects must be utilized instead. Several bugs as well as any materials they create or leave behind, including their dead bodies, may be used to determine their present stage of development and their generational history.

With this information, entomologists determine when they first arrived on the corpse. This also reveals the time at which the stage of decay associated with their presence began.

However, determining the age of a corpse is often not this straightforward. Often, other factors come into play that affect insects and therefore affect the data they provide.

Factors Affecting Insect Access to a Body

If a person dies in an area to which bugs have limited access, the time it became infested will be later than the time of death. If individuals are rendered unconscious or become paralyzed before death, they could become infested while still alive.

However, in instances where neither of these hold relevance, time of infestation may be considered representative of time of death.


Temperature Changes

Temperature plays a key role in all calculations. This is because flies and beetles develop more quickly in warmer surroundings. Luckily, the effect of temperature on growth rate has also been meticulously studied. By estimating the past temperatures to which a body has been exposed, experts can determine the rates of growth during each previous hour. Working backwards, hour by hour, they can then find the likely time of infestation.

Another important element is the climate within a corpse itself. Bodies will be different temperatures based on whether or not they are in clothing, wrapped within other materials, or completely uncovered and exposed to the elements. They may be found in buildings, vehicles, or outdoors, all with different levels of temperature variability.

Even the action of maggots feeding on part of the body may raise that area to a higher degree, causing various changes.

In Conclusion

The process of forensic entomology is a complex one, and requires a lot of calculation and detective work. If any element is left out results can be rendered inaccurate. Intense attention to detail is necessary, but when performed optimally and within the ideal time frame, yields highly precise results that can be used persuasively in criminal cases.


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