Forensic Entomology

What is Forensic Entomology?

Forensic Entomology is the use of the insects, and their arthropod relatives that inhabit decomposing remains to aid legal investigations. The broad field of forensic entomology is commonly broken down into three general areas: medicolegal, urban, and stored product pests. The medicolegal section focuses on the criminal component of the legal system and deals with the necrophagous (or carrion) feeding insects that typically infest human remains. The urban aspect deals with the insects that affect man and his immediate environment. This area has both criminal and civil components as urban pests may feed on both the living and the dead. The damage caused by their mandibles (or mouthparts) as they feed can produce markings and wounds on the skin that may be misinterpreted as prior abuse. Urban pests are of great economic importance and the forensic entomologist may become involved in civil proceedings over monetary damages. Lastly, stored product insects are commonly found in foodstuffs and the forensic entomologist may serve as an expert witness during both criminal and civil proceedings involving food contamination.

How diverse is forensic entomology?

Here are a few examples: The diverse applications of forensic entomology include the detection of abuse in children and neglect of the elderly. Published cases exist that detail parents intentionally using wasps and bees to sting their children as a form of punishment. Additionally, entomological evidence has been used to prove neglect and lack of proper care for wounds existing on the elderly under both private and institutional care.

It is theorized that the stings (or mere presence) of bees and wasps may be responsible for a large number of single occupant car accidents that seem to lack a definitive cause. In addition to automobile accidents, insects have been suspected of causing aircraft crashes through the obstruction of essential instrumentation, and even implicated in the obstruction of fuel lines causing engine failure. Forensic entomologists are also requested to examine the fragmented remains of insects that have impacted and lodged on the front fascia, windshield, and radiator of automobiles. Analysis of such remains can yield evidence to the probable path of an automobile through particular areas when pinpointing the location and areas of travel are of unique importance.

Insects can also affect the interpretation of blood spatter pattern analysis. Roaches simply walking through pooled and splattered blood will produce tracking that may not be readily recognizable to the untrained observer. Specks of blood in unique and unusual areas (such as on ceilings) may mislead crime scene technicians unless they are aware of the appearance of blood contaminated roach tracks. Similarly, flies and fleas may also track through pooled and spattered blood. However, flies will also feed on the blood and then pass the partially digested blood in its feces, which are known as “flyspecks”. Flies will also regurgitate and possibly drop a blood droplet on a remote surface, which may serve to confuse bloodstain analysis. Fleas feeding on the living pass a large amount of undigested blood (used as the larval food source) on many household surfaces. If a crime occurs in a heavily infected apartment, fecial drops already present would serve to confuse analysts as those droplets would test positive for human blood. Therefore it is important to recognize and properly document the natural artefacts that may occur from the presence, feeding, and defecation of roaches, flies, and fleas. Insects that feed on living, decomposing, or dried vegetable material are submitted to the forensic entomologist in an effort to determine the country or point of origin. This is particularly important with vegetative material such as imported cannabis.

What information can a forensic entomologist provide at the death scene?

Forensic entomologists are most commonly called upon to determine the post-mortem interval or “time since death” in homicide investigations. The forensic entomologist can use a number of different techniques including species succession, larval weight, larval length, and a more technical method known as the accumulated degree hour technique which can be very precise if the necessary data is available. A qualified forensic entomologist can also make inferences as to possible post-mortem movement of a corpse. Some flies prefer specific habitats such as a distinct preference for laying their eggs in an outdoor or indoor environment. Flies can also exhibit preferences for carcasses in shade or sunlit conditions of the outdoor environment. Therefore, a corpse that is recovered indoors with the eggs or larvae of flies that typically inhabit sunny outdoor locations would indicate that someone returned to the scene of the crime to move and attempt to conceal the body.

Similarly, freezing or wrapping of the body may be indicated by an altered species succession of insects on the body. Anything that may have prevented the insects from laying eggs in their normal time frame will alter both the sequence of species and their typical colonization time. This alteration of the normal insect succession and fauna should be noticeable to the forensic entomologists if they are familiar with what would normally be recovered from a body in a particular environmental habitat or geographical location. The complete absence of insects would suggest clues as to the sequence of post-mortem events as the body was probably either frozen, sealed in a tightly closed container, or buried very deeply.

Entomological evidence can also help determine the circumstances of abuse and rape. Victims that are incapacitated (bound, drugged, or otherwise helpless) often have associated fecial and urine soaked clothes or bed dressings. Such material will attract certain species of flies that otherwise would not be recovered. Their presence can yield many clues to both antemortem and post-mortem circumstances of the crime. Currently, it is now possible to use DNA technology not only to help determine insect species, but to recover and identify the blood meals taken by blood feeding insects. The DNA of human blood can be recovered from the digestive tract of an insect that has fed on an individual. The presence of their DNA within the insect can place suspects at a known location within a definable period of time and recovery of the victims’ blood can also create a link between perpetrator and suspect.

The insects recovered from decomposing human remains can be a valuable tool for toxicological analysis. The voracious appetite of the insects on corpses can quickly skeletonise the remains. In a short period of time the fluids (blood and urine) and soft tissues needed for toxicological analysis disappear. However, it is possible to recover the insect larvae and run standard toxicological analyses on them as you would human tissue. Toxicological analysis can be successful on insect larvae because their tissues assimilate drugs and toxins that accumulated in human tissue prior to death.