Entomology

Forensic entomology is the study of insects as it relates to the criminal justice system. [1] There are three subdisciplines of forensic entomology: [1]

Minimum PMI + CROP + Time of Death Calculations

  • The estimation of the age of the oldest specimen found on the body

  • Then verifyin

Stages of Flies (Maggots)

  • 1st Instar

  • 2nd Instar

  • 3rd Instar

  • Adult Stage

  • Urban entomology: focuses on controversies arising from insects in the human environment. [2] This can include:

  • Lawsuits [2]

  • Nursing home neglect [2]

  • House damage [2]

  • Pet neglect [2]

  • Stored products entomology: focuses on disputes of insects or insect parts in food and other products. [2] Examples include:

  • Caterpillars in cans of vegetables [2]

  • Maggots in fast food meat [2]

  • Insect debris in cereals [2]

  • Medicolegal (medicocriminal) entomology: focuses on using insect succession and insects found at a crime scene to help determine the timing of events. [3]


Using Insects to Determine Time of Death

The most important application of medicolegal entomology is the determination of the postmortem interval (PMI), or the time since death. [3, 4] This is accomplished by studying the succession of insects on a corpse. [3, 5] Insect succession is the predictable time and species profiles on human and animal remains given specific environmental conditions. [6]

There are two main methods for using insect succession to determine PMI: [5]

  • Using successional waves of insects: This method is used when the corpse has been dead for between a month up to a year or more. [5]

  • Using maggot age and development: This method is used when death occurred less than a month prior to discovery. [5]

The first insects to arrive at a corpse are usually blowflies (Calliphoridae) and flesh flies (Sarcophagidae). [6] Blowflies can arrive at a body within 15 minutes of death. [6] Once the fleshy material is gone, other insects, such as beetles, arrive. [6]

Factors Influencing Insect Activity

There are several factors that can influence the number, type, appearance, and life cycles of insects found on a corpse: [7, 8]

  • Temperature: Insects are poikilothermic, meaning that their body temperature is dependent on the surrounding temperature. [7] In warmer environments, insects develop faster than in cooler environments. [7]

  • Habitat: Different species of insects are found in different habitats. [6] For example, some species of blowflies are more common in urban areas, while others are more common in rural areas. [9-11]

  • Season: Different species of insects are active at different times of year. [6] For example, blowflies are more active in the summer than in the winter.

  • Drugs: The presence of drugs in a corpse can affect the development of insects. [4, 12] For example, cocaine has been shown to accelerate the development of blowfly larvae.

  • Geographic location: Different species of insects are found in different geographic locations. [13]

Forensic Entomologist's Role

A forensic entomologist can determine the following information in the event of a crime in which insects are present: [4, 13]

  • Minimum time since death (PMIMIN): By studying the age and development of the insects on a corpse, a forensic entomologist can estimate the minimum amount of time that the person has been dead. [4]

  • Possible site of trauma: Insects are attracted to wounds, so the presence of insects on a particular part of the body can indicate the location of a wound. [4]

  • Geographic origin of death: If the insects found on a corpse are not native to the area where the body was found, this can indicate that the body was moved after death. [4, 13]

  • Toxicology: The presence of drugs in a corpse can be determined by analyzing the insects that have fed on the body. [4]

  • Identify the victim (in the absence of a body): In some cases, the insects found on a piece of clothing or other object can be used to identify the victim, even if the body is not present. [4]

Insect Collection at Crime Scene

The scene of remains is treated and processed like a crime scene. [14] Orderly, careful search that may utilize various detection methods are used. [14] Because collecting evidence is usually intrusive, it must be done carefully. [15] Documentation should be completed when sampling from the body and this should be explicitly stated to the death investigator. [15]

Important things to note at the scene: [15]

  • Photographs and notes of the general scene and habitat

  • Photographs and notes on the insect infestation on the remains

  • Collection of meteorological data

  • Collection of adult flies and beetles above the remains

  • Collection of eggs, larvae, and pupae on the remains

  • Collection of specimens in the surrounding area of the body (~20ft)

  • Collection of specimens under the remains

  • Collection of soil samples with a specific note on the location (i.e. under the head)

  • Notes on the ecological characteristics of the scene

  • Collection at autopsy

  • Retrieval of historic weather data

Important Insect Orders in Forensic Entomology

  • Flies (Diptera): Blowflies, flesh flies, and muscid flies are the most useful flies in forensic investigations. [10]

  • Beetles (Coleoptera): Hide beetles, rove beetles, and carrion beetles are common beetles found on corpses. [16, 17]

Stages of Insect Growth and Development

Insects grow by going through stages called instars, starting with the egg and finishing as the adult stage. [7] The cycle stages are egg, 1st instar, 2nd instar, 3rd instar, pupa, and adult. [4] Insects shed their skins (molt) at certain developmental time periods in order to grow. [7]

Decomposition and Insect Activity

Decomposition of a corpse begins soon after death and may be evident within 2-3 days. [18] The four main stages of decomposition are: [19, 20]

  • Fresh: During autolysis (enzymes begin to break down tissues), which lasts about a day or two [20]

  • Bloat: Gasses within the body put pressure on the walls of the body [20]

  • Active Decay: Fluid begins to release through openings in the body; nose, eyes, or breaks in the abdominal wall indicate the start of this process; maggots begin to feed [20]

  • Advanced Decay: Maggots leave due to a lack of materials and fluids; decay slows down [20]

  • Dry/Remains: Most of the body's soft tissues have decomposed, leaving bones, hair, cartilage, and an accumulation of wet, sticky material called byproducts of decay [20]

Different insects are attracted to different stages of decomposition. For example, blowflies are attracted to fresh corpses, while beetles are attracted to corpses in later stages of decomposition. [6, 17] The points of entry for insects on a dead body include any openings such as the nose, mouth, eyes, and wounds.

The decomposition process can be slowed down by a number of factors, including:

  • Cold temperatures

  • Burial

  • Wrapping

Animal Models for Human Decomposition

Pigs are often used as animal models to represent human decomposition. [12] This is because pigs have a similar body size and composition to humans.