Forensic Entomology

Editor’s Note: This article originally appeared in Entomology Today, a project of the Entomological Society of America with the goal of reporting interesting discoveries in the world of insect science and news from various entomological societies. To learn more, visit www.entomologytoday.org.

Every respectful movie or TV show featuring a scene with a dead body makes sure the buzzing of the flies hovering over the body is clearly heard. If the scene becomes particularly gruesome, the unmissable maggots feeding on the body are shown, making the hair of the most sensitive viewers stand up.

As dramatic as these images can be, they are actually a semi-clear representation of what actually happens to a dead body when it becomes “available.” Necrophagous and necrophilous insects start to arrive on the body minutes after death and start checking it out to see if it would be a suitable place to colonize.

BLOW FLIES. The first and probably most important group that detects the body and starts colonization is Diptera, more commonly known as flies. One of the main families of flies observed around decomposing matter is Calliphoridae, or blow flies. Blow flies are those metallic flies we see often around road kill or even near our garbage bin when we take out the trash. They are medium-sized flies (you definitely don’t need a microscope to see them!) and are normally metallic blue or green; this is why some species’ common names include blue bottle flies and green bottle flies.

Blow flies arrive on a body or any other type of organic decomposing matter, taste it with their sponging proboscis and, once they feel it is a suitable place to lay eggs, oviposit clusters of eggs in natural orifices, so that the eggs are moist and protected. From these eggs, after a time that depends on the species of fly, season, temperature, weather conditions, relative humidity and several other variables, little first instar larvae emerge. These tiny worm-like creatures are incredibly voracious and start immediately to consume the body. They molt twice, respectively into second instar and third instar, and their size increases significantly throughout their larval development.

Once the maggots have fed enough, they leave the body, which at this point probably has little left to offer, and migrate toward a dry place where they pupate. The maggot’s cuticle (the outmost “layer” of their body) hardens and becomes darker, and the pupating fly shrinks in size and assumes an oval appearance. Blow fly pupae don’t move, and they remain in that stage until the adult fly inside is ready to emerge. Because of their appearance, it is common for pupae to be overlooked or mistaken at the scene for mice droppings.

After the pupal stage is complete, an adult fly emerges from the pupa, leaving an empty puparium (case). Newly emerged flies are still not fully pigmented, so their coloration is clearer, and they have their wings still folded over their body. At this point, they have a somewhat spider-like appearance.

MORE DIPTERA (FLIES). Another important family of flies is the family of Sarcophagidae. These flies are quite large and are easily recognizable with a naked eye for their typical color pattern: black and gray stripes on the thorax and a checkered abdomen. Fun fact about Sarcophagidae: Instead of laying eggs, they actually birth larvae!

Muscidae is another common Diptera family; these flies are simply our common house flies and are similar to Calliphoridae but rarely display metallic colors.

Smaller but quite common as well are cheese skipper flies, or Piophilidae. The peculiarity of this family lies in the fact that their maggots, typically observed on wet remains, don’t just crawl — they jump! As a defense mechanism, these little larvae use their body to propel themselves in the air. Fun fact about Piophilidae larvae: They are also known to be pests of cheese and ham, and in Italy they make a special type of cheese, casu marzu, which is left to be colonized by Piophilidae on purpose! The cheese is eaten along with thousands of little jumping maggots and the taste is simply amazing (or so they say).

COLEOPTERA (BEETLES). Along with Diptera, another major group of insect is commonly found around remains: Coleoptera, or beetles. A few families of beetles are attracted to decomposition because they feed directly on the remains or because they actually feed on the maggots that are already there.

Silphidae, also known as carrion beetles or burying beetles, are a family of Coleoptera typically observed around remains. They are usually large insects and can show a wide variety of shapes and colors; typically, they come to the remains to feed on Diptera eggs or larvae and therefore are defined as opportunistic predators.

Staphylinidae, or rove beetles, are another significant forensically interesting family. They are normally elongated beetles, with very short forewings and the ability to move quickly once they are disturbed or sense some danger. Some Staphylinidae can bend their abdomen forward, like a scorpion does, and sting.

Hister beetles, Histeridae, are also quite common around carcasses. They can be metallic and their color can range from shiny black to greenish brown; they are usually round and their forewings are a little shorter than their abdomen, but not as short as Staphylinidae.

Also sometimes found at a scene of decomposition: Nitidulidae, or sap beetles, which are smaller beetles with an incredible variety of shape and colors, having in common their clubbed antennae. Similar in size, Cleridae beetles can also be found; they are easily recognizable by their pronota (their “necks”), which are narrower than their heads.

Of course, many more groups, orders, and families have been observed in successional studies or in casework. Their presence depends on the location of the body, whether or not the body is indoors or outdoors, the presence of a water environment, the flora around the scene, the season, and so on.

The previous descriptions are not a comprehensive list of insects of potential forensic interest, but rather they are just the most common ones that have been documented so far.

Every respectful movie or TV show featuring a scene with a dead body makes sure the buzzing of the flies hovering over the body is clearly heard.

Denise Gemmellaro is a graduate student in entomology at Rutgers University and director of the Forensic Entomology Workshop held at the New Jersey School of Conservation, a two-week summer program for students and industry professionals to gain hands-on experience in the fundamentals of forensic entomology.