Forensic Entomology

 

Insects make up the dominant life form on the planet (eight out of ten animals [by species] are insects; more than half of all known living things [by species] are insects), so it is little wonder that they may be found during the course of a variety of types of forensic investigations. Forensic entomology, the use of insects as evidence, has a long and rich history stemming back to ancient China. Medicocriminal entomology, the branch of forensic entomology dealing with human death, is an established science which has been used to estimate the time, location, cause, and manner of death in cases of homicide, suicide, and accidental deaths throughout the world. Medicocriminal entomology is applied in the investigations of hundreds of human fatalities every year and has recently become the topic of TV dramas, although it rarely portrayed accurately.

When applied to forensic investigations, the primary use of entomology is to estimate the time since death, or postmortem interval (PMI) during death investigations. Although questions related to the location or manner of death may also be addressed using entomological evidence, the vast majority of forensic entomology cases continue to focus on PMI estimates. After a period of 24-48 hours, forensic entomology is one of the few methods for accurately estimating the PMI and entomological analysis has been successful for estimating the PMI after many years have passed. Flies, particularly blow flies (Diptera: Calliphoridae) are the first animals to locate and colonize a dead animal, often within seconds or minutes after death when conditions are favorable. The adult flies deposit eggs on the body, which then hatch into maggots, the stage that is responsible for removing much of the soft tissue on terrestrial bodies. After feeding, maggots migrate from the body to pupate, from which the adult will emerge. Because insects are cold-blooded, their rate of development varies with the environmental temperatures; that is, (generally speaking), the warmer it is the faster the insects will develop and the cooler it is the slower they will develop. Therefore, by knowing the species of fly, the stage of development, and the temperatures that the insect experienced during development, a forensic entomologist may accurately estimate the age of a particular insect found on a body. Because the delay between death and colonization are often minimal, this knowledge may be applied to the PMI of a body and an estimate of PMI may be made. By knowing the ecological habits of the insects, inferences related to the specifics of a case may be made, such as the effects on insect colonization of a body found indoors.

 

As a board-certified forensic entomologist, I regularly consult with various law enforcement agencies as well as private attorneys from across the country and the world on a wide variety of cases. If you are in need of assistance with a case I can be contacted directly using the information on the main page.

 

 

 

The blow fly Calliphora vicina feeding on liver in the laboratory. Blow flies are attracted to dead bodies immediately after death and begin laying eggs shortly after arriving. You can see fly eggs in the lower right hand corner of the photo.

Blow flies lay around 200-300 eggs at a time, but work together to deposit large egg masses (numbering in the thousands). These flies (Phormia regina) have carpeted one area of this pig with their eggs by gluing them to the skin and to each other.

Maggots are just baby flies, but they have a reputation for being disgusting. The slime which they produce actually has anti-microbial properties that limit the growth of bacteria (one of the reasons these same maggots are used for “maggot therapy” or surgical myiasis).

Those are not maggot eyes looking at you; those are the maggots’ spiracles, the openings to their respiratory systems. Maggots are just like you and I in that they breathe oxygen. The maggots are able to feed continuously in a head-down position because they breathe through their posteriors.

When maggots finish feeding on a body they crawl away and pupate. Their exoskeletons harden to form a puparium, a chrysalis-like protection for the developing pupa inside. The puparium darkens with age, and the progression of this darkening can easily be seen in this group of puparia.

How does a fly get out of its puparium? Flies have a structure called a ptilinum in their head, a balloon-like sack that inflates with hemolymph (blood) to break the operculum of the pupal case. Flies also use this structure to dig to the surface if they had burrowed into the soil as maggots. When they are free, the ptilinum retracts back into the head and is never used again.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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