Module 6 - Forensic Anthropology and Forensic Entomology (Bones & Bugs)

Pig Remains Infested by Blowflies

- Source: Courtesy Department of Entomology,
University of Nebraska-Lincoln, and Jim Kalisch, UNL Entomology

The information about insect colonization patterns or insect succession that forensic entomologists use to investigate homicide cases comes from data collected from scientific research studies. Because insect species and weather conditions vary from one climate to the next, research data from one geographic area (such as mixed boreal forest) cannot be applied to another geographic area (such as subtropical). Therefore, forensic entomologists use insect succession data that comes from the same geographic region as the region in which the body was found. Because homicide victims can be found in various geographic regions, numerous scientific research studies about insect succession must be completed to help forensic entomologists assist in criminal investigations. In 1996, the Canadian Police Research Centre (CPRC) began establishing a database that contains information about insect succession from each of the major biogeoclimatic zones in Canada.

One of the CPRC insect succession studies was completed in 1999 near Edmonton by Dr. Gail Anderson and Dr. Owen Beattie. The Edmonton area was chosen for this study because it is located within the mixed boreal forest zone, the biogeoclimatic zone with the highest human population in Alberta.

Instead of using human remains, pig carcasses from local farms and slaughterhouses were used to model humans. Pigs were used because their overall size and the position of their internal organs are similar to the human body. In another attempt to simulate how human remains may be found in forensic cases, some of the pig carcasses were dressed in human clothing. To prevent small animals such a coyotes from eating the dead pigs, they were covered with wire mesh.

To simulate further various conditions in which human remains may be found in a forensic investigation, the pig remains were studied in eight different types of conditions: sun, shade, spring and summer, autumn and winter, partially buried, and completely buried.

Sun vs. Shade

When forensic entomologists compared the decomposition of several pig carcasses left in the sun with several pig carcasses left in the shade, the following were discovered:

• The same type of fly species and beetle species invaded the dead bodies left in the sun and shade. However, decomposition by insect succession took longer in the shade.

• Masses of maggots infested the head first in the dead bodies left in both the sun and shade.

• A greater number and a greater variety of insects were found upon the pig carcasses left in the sun compared to the pig carcasses in the shade.

Spring and Summer vs. Autumn and Winter

When researchers compared the decomposition of several dead pigs during the spring and summer with several dead pigs during the autumn and winter, the following were observed:

• The most abundant fly species to infest the pigs in the spring/summer was a type of blowfly known as Protophormia terraenovae. The most abundant species of fly to infest the pigs in the autumn/winter were ‘cool weather flies’ also known as Phormia regina.

• It took 6 days before fly eggs were laid upon the dead bodies observed in the autumn whereas flies laid their eggs upon the dead bodies within 24 hours during the spring and summer.

• In the dead bodies studied during the autumn, fly eggs did not mature into maggots likely because of an early snowfall that caused cold temperatures and high humidity. In contrast, fly eggs consistently matured into maggot masses in the dead bodies studied in the spring and summer.

Partially Buried vs. Completely Buried

Some of the pig bodies were left on the ground and partially buried under tree branches while several other pig bodies were completely buried in graves 20-30 cm deep. When scientists compared the decomposition of the partially buried pigs with the decomposition of the completely buried pigs, the following were noted:

• In the partially buried bodies, blowfly colonization followed by beetle infestation occurred in a predictable fashion. In the buried bodies, beetle infestation was predominant.

• After 15 days, decay had occurred in the face and head region of the partially buried bodies while decay was isolated to only the feet in the completely buried bodies.

• After 30 days, most of the flesh and skin on the partially buried bodies was gone and skeletal remains were visible. After 30 days, the flesh and skin was still present in the buried bodies, but they appeared bloated. Bone was not visible.

• Decomposition caused by insect infestation took longer in the bodies that were completely buried than in the bodies that were only partially buried.