Forensic Entomology: Using Insects in Investigations
What is Forensic Entomology?
Different bugs are present on a corpse during each stage of its decomposition. Using facts known about these insects, scientists can discover information about the body they are infesting.
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
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 of the remaining body.
Bugs Verify the Scene of the Crime
A corpse and the bugs infesting it must link directly to a believed crime scene. It should make sense why each insect is present, considering the location. If there are inconsistencies, the person may have died in another area, and investigators must keep looking to discover where.
Bugs Determine Time of Death
The precision with which time of death can be estimated is highest when bodies are discovered within a 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 blowfly has been well studied and the length of each of its main developmental stages has been scientifically determined. Based on the stage of 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
Bodies in later stages of decay lose moisture and no longer have blowflies. In this case, other insects must be utilized instead to gain any useful information. These and the materials they create or leave behind help determine their present stage of development as well as their generational history.
With this information, entomologists determine when they first arrived on the corpse. This also reveals the time at which the later stage of decay associated with their presence began.
However, determining the age of a corpse is often not 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 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.
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, it yields highly precise results that can be used persuasively in criminal cases.