The Secret Life of Insects
Blood splatter patterns, DNA profiling, bite marks, and ballistics. Each of these has played an important part of forensic criminology within the past few years. One forgotten aspect of forensics is forensic entomology (American Board of Forensic Entomology 2004). Forensic entomology refers to the study of insects and other arthropods that are believed to pertain to criminal events in order to discover useful information to an investigation (The Scientist 2001). In a 2004 survey, 93 percent of those individuals surveyed were able to explain what forensic science entailed but only 13 percent could offer a general explanation of forensic entomology (Annual Review Entomology 1985). These results clearly show a need for further research into this science, in spite of the multiple research studies that have already been conducted. Insects are fascinating creatures and have many things to tell us if we’re only willing to take the time and listen.
The first documented accounts of the usage of forensic entomology are from China during the 1300s. A man was murdered with a sickle and an officer brought in the local farmers with their sickles. Only one sickle attracted flies to it and that man broke down and confessed to the murder. In 1855, a physician was able to prove that the death of a child took place years earlier by the use of insects found within the dead body. In spite of these ancient uses, the first Ph.D. in forensic entomology was not earned until 1991 at Purdue University and today only a handful of professional forensic entomologist exist in the world (The Scientist 2001). Forensic entomology is an extremely useful field and further research need to be conducted for its full potential to be realized.
Modern forensic entomology can be used to determine the time of death and whether or not a body has been moved following death. Blowfly eggs are extremely useful in estimating the time of death if discovered on a body. By knowing how long it takes for blowfly eggs to hatch and larvae to fully develop the time of death can be easily estimated. By doing studies using non-human carrion it can be determined when insects arrive on the body and exactly when after that they begin to lay eggs. Once the eggs have been hatched, the course follows a distinct pattern of development. Other uses for forensic entomology include location of death. If a body is discovered in a warm environment that is housing an insect that is usually found in cooler environments, this is a sign that the body could very well have been relocated after the victim was killed (ESA Bulletin 1985).
Insects obviously play a crucial role in forensic entomology. These are the prime indicators for determining the approximate time of death. The two main types of insects that predominately prey upon human flesh are Diptera (true flies) and Coleoptera (beetles). Diptera is further divided into muscid flies, blowflies, and flesh flies. Important members of Coleoptera include skin beetles, carrion beetles, and rove beetles (JFSCA 1983). It is important to follow appropriate techniques in order to prevent any tampering of the evidence. Special care must be taken in preserving as well as identifying all specimens.
Insects are collected from on, in, or underneath the corpse. All adult forms are immediately killed and preserved using a solution of 70% ethanol. Flying insects are captured using a short handled net, crawling insects with forceps, and burrowing insects by shallow digging (including a small sample of the soil they inhabited with the specimen). Immature insects are collected in two samples. One group of immature insects is killed and preserved using the soft-bodied insect method where specimens are placed in a solution of refined kerosene, acetic acid, and ethyl alcohol. The other group of immature insects is collected and kept alive to be reared to adulthood in the laboratory. As it can be extremely difficult to identify immature insects from one species to another, rearing must be used to determine the species once full maturation is complete. Approximately 100 immatures are needed in order for proper rearing to occur outside of their natural environment (JFSCA 1983).
Identification of insects involves distinguishing between the three different larval stages, called instars. An instar is one of the stages of immature insects in between molts. Entomologists determine speciation in the insects by looking for distinguishing characteristics in spiracles, reproductive organs, and mouthparts. Cocoons are often looked at as well (The Scientist 2001).
Although numerous studies have been conducted using animal carcasses to study the rate at which insects affect decomposition, there is one project that stands out amongst all others. In 1962, Jerry Payne used infantile Sus scrofa (pigs) in Clemson, South Carolina to determine how much involvement insects have in decomposition and how that information can be used in modern day criminal cases (Ecology 1965).
The first major step in beginning any research involving forensic entomology is to choose the appropriate animal to use as carrion. In this study, pigs were chosen to be the animal of study because they were found to be the most efficient organism for studying decomposition rates and insect scavenging. Earlier studies involving cats and dogs were hard because those carcasses are not readily available. Birds proved to be too difficult to study for insect activity due to the amount of feathers. Pigs, however, are relatively easy animals to obtain, they are of a large size, and they have no feathers.
Each animal was placed within a 4x4x2-foot wire cage to prevent predation of other animals. Special cages were also used that included a wire mesh covering over the cage in order to prevent insects from entering the cage. This second type of cage was used for the control pig, to determine just how much damage is caused by the insects versus a carcass without insect activity. Initially these corpses were monitored at 8-hour intervals. The physical condition was recorded with special interest in odor, fluids, bloating, and the amount of decomposition that had taken place.
Once the pigs were placed out in the wooded location, the decomposition was monitored and divided into six different stages, fresh, bloated, active decay, advanced decay, dry, and remains stage.
The fresh stage began as soon as the animals were taken from the freezer and continued until signs of bloating became evident. The only odors at this stage were associated with pig mash and straw. The first insects to appear were the sarcophagids (flesh flies) followed by the calliphorids (bottle flies). These arrived after approximately 10 minutes and fed on the wet, moist areas. Vespidae (yellow jackets) arrived shortly thereafter and fed on juices from the body as well as some of the calliphorids themselves. Eggs were deposited by both the sarcophagids and calliphorids while the body was still partially frozen, which was up to 6 hours for most of the carcasses. Formicidae (ants) and Phalangiidae (daddy longlegs) were the last insect species to make an appearance on the pigs on the first night.
The second stage, the bloated stage, began on the second day after placement. This stage is characterized by the first signs of bloating around the abdomen and the pooling of blood on the underside of the body. Many more calliphorids appeared on the second day and sarcophagids were still depositing eggs. New insects included the Piophilidae (skippers) and Lonchaeidae (lance flies). Burrowing insects arrived for the first time at dusk on the second day. Scarabaeidea (scarab beetles) often came out from underneath the corpse to feed during the second night; they remained in the soil during the day feeding on the juices that were absorbed into the soil. Odors were now of the decomposition of the body and the skin of the pig begun to tighten across the body as gases and fluids leaked out. New insects that arrived on the third day include Drosophilidae (flies), Coreidae (squash bugs), and Stratiomyidae (soldier flies). Larvae began feeding around the mouth, nose, and anus. These maggots also aided in the release of gases from the body by tunneling through the skin. The majority of the insects left during the night, leaving mainly Formicidae and Histeridae (histerid beetles). Other adult insects inhabiting the corpse consumed many of the newly hatched larvae.
By the fourth day the active decay stage had begun. Calliphorids and Muscidae (house flies) had increased greatly and Silphidae (burying beetles), Sepsidae (black scavenger flies), and Otitidae (picture-winged flies) were first observed on the carrion. All larvae were actively feeding upon the carcass by the fourth day. Yellow jackets were in high numbers as well. On the fifth day, Bombus impatiens (bumblebees) were found feeding on the fluids of the body as well as a few species of wasps. The flesh of the head and other moist areas of the corpse had been completely removed, leaving only skin and bones. Liquefaction was evident as well as extremely strong odors of decay. Larvae were mostly active in the chest and abdominal regions, maggots being the most dominant of the immature insects. Coleoptera was the most prevalent order of mature insects that dominated the active decay stage. At dusk, the family Sphingidae (moths) made its first appearance, consuming fluids from the corpse.
The advanced decay stage mainly took up the sixth and seventh days of decomposition. All odors were beginning to fade and very little flesh was still on the body. Immature insects began to leave the corpse as their supply of nutrients was becoming depleted. Burrowing insects were also beginning to migrate from the carcass, leaving behind tunnels in the soil around the body. By the seventh day, the body was completely dry. A few calliphorids were feeding upon the small amount of remains, but almost all other insects had left the body.
The dry stage began on the eighth day and lasted for the next three weeks. At this stage only dry skin and bones were left of the body and the only odors were of dry skin and wet fur. Any larvae that were alive at this stage could not complete their development due to the lack of food. There was minor ant and beetle activity, carrying away small scraps. In the final week of the dry stage, non-carrion insects began to use the remains of the corpse for shelter. The only time insects were readily feeding upon the body was when the body became wet after a summer storm, bringing back original families such as Drosophilidae.
The final stage of decay is the remains stage, now three weeks after the initial placement in the chosen environment. It was very hard to distinguish between where the dry stage ended and the remains stage began, both were extremely similar. The only odors that were present in the area were normal to the woodland area. The only remains that were left of the decomposed carrion were hair, bones, and teeth. The only insects in the area were normal inhabitants of the area and were non-carrion feeding insects (Ecology 1965).
In summary, Diptera was the first group to colonize the body, having its peak appearance in the very early stages. Members of Hymenoptera (bees and wasps)and Coleoptera were the next to arrive along with some incidental insects (Forensic Science International 2001). Incidentals are those insects that are non-carrion feeding insects whose appearance is considered to be only coincidental; these are not counted as insects helping with the decomposition of the corpse. By conducting studies such as this, the arrival and departure times can be noted and applied to criminal investigations.
Entomology plays a very important role in forensic science. For hundreds of years insects have been used within the law enforcement to help solve criminal cases but it has yet to become widely appreciated. By using proper collection and identification techniques insects can be appropriately used as evidence within criminal investigations. With new research being conducted using animal carrion, more and more information can be obtained that will only add to the importance of insects.
