What is forensic entomology?

Forensic entomology is the branch of forensics dealing with the use of insects and arthropods as living evidence in crime investigations and legal matters. One the most important purposes of forensic entomology is determining the minimum time since the person is dead, also referred to as minimum post-mortem interval or PMI. The start of this interval is marked by the time when the insect first laid its eggs on the body, and its end is determined by the discovery of the corpse and the identification of life stage of the specie that first infested the body. The probable period of time the person has been dead can be accurately calculated and measured by considering the duration of the specie’s life stage along with the stage of decay.

Insects and body decomposition

Blowflies, flesh flies, cheese skippers, hide and skin beetles, rove beetles and clown beetles, are all insects used by forensic entomologists as evidence and clues for investigations. According to entomologists, some species consume a dead body when they are only in their juvenile stage. We call them carrion feeders since they live on dead and rotting flesh. Other carrion feeders can consume a body during their juvenile and adult stages. Such organisms are called necrophages. These insects also attract other species to the body as they serve for food for these species. Blowflies are the primary insects used in forensic entomology. They belong to the family of Calliphoridae, widely spread in Europe and Britain. These insects are the first to colonize a dead body after few hours of death. That’s why an accurate measure of PMI can be obtained after calculating the age of the oldest blowflies present. Other insects can serve as PMI indicators but they are less precise since they arrive to the body after blowflies. Beetle, fly, moth, wasp are examples of such insects.

Adult blowflies can easily find cadavers by tracking down the odours of the body. These insects lay their eggs either in dark and moist places for example under the body or in the folds of clothes, or in the natural orifices such as the nose, ears, mouth, and eyes. When the eggs hatch, a first instar larvae is obtained. During its growth, it moults twice and passes through two stages: second and third instar larvae.

Sometimes insects don’t stay on the body, they move away to other sites such as the soil, under rocks or even under carpets and furniture. Also, insect pupa can be found on the body or next to it, so it is essential to collect them too.

What are the challenges that forensic entomologists face?

Forensic entomologists are not always the first to arrive to a crime scene. Death investigators may find a body but would contact the forensic entomologist after days or even months. The insect evidence would be collected by non-professionals which can cause a big problem since the forensic entomologist would have to depend on others who might not be trained well enough or even lack experience in recognizing and collecting such evidence. This may lead to inaccurate investigations based on the damage or lack of specimen. Contacting the forensic entomologist should be done immediately but since discovering corpses can be accidental, death investigators that first arrive to the crime scenes should be well trained in order to provide the minimum assistance required outside their fields of specialization.

Another challenge faced by forensic entomologists is determining the climatological data, and specifically the temperatures, intensity of rainfall, fog conditions, cloud cover, and time of sunrise and sunset. Knowing these information helps determine if insect colonization (especially blowflies) is immediate or if there has been a delay in the insects finding or laying eggs on the corpse. Every insect development is effected by the temperature. The higher the temperature is, the faster the insect develops and vice versa (the graph is relative to blowflies). If the ambient temperatures during the period of development are known, then, in theory, the minimum PMI can be determined. But when significant time has passed, environmental conditions may have changed considerably, so confirmation of climatic conditions at the scene may be impossible.

Usually, with bodies in outdoor environments, the data are available from weather data collected by weather stations. The selection of a weather station or stations for data regarding a specific death scene is of great importance. If the temperatures go below 0°C (32°F), and negative numbers are present, the calculations will suggest that the growing maggot is becoming younger the longer the numbers are in the negative column. This is not biologically possible. When the maggots are in an aggregation known as the maggot mass, they generate great amounts of exothermic heat. This is primarily seen during the entire third-instar duration until they move from the remains to initiate migration. Research has shown that when given a range of temperatures to choose from, third instar blowfly maggots will select a temperature of approximately 90°F. This also is very close to the temperature that provides for the fastest growth. This effect may not be of major significance when ambient temperatures are in the 80s and 90s, but will be of great importance to consider when development is progressing with temperatures in the 30s and 40s. In cases where remains have been recovered and the body placed in the morgue cooler over a weekend prior to autopsy, maggot mass temperatures are still in the 85 to 90°F range after 48 hours of exposure to 40°F temperatures in the cooler. Therefore, factoring in a temperature of approximately 90°F for 24 hours or so may help compensate for these added energy units. In addition, if 90 to 95°F is at the fastest rate of development, then what has been calculated is the shortest period of time available for growth. Any other temperature would produce a longer period for the development of the maggot. Given the importance of temperature knowledge, electronic temperature data loggers should be placed not only at crime scenes for the readings to be compared with data from the meteorological station over the same period to estimate the temperatures during that period at the scene of the crime, but also permanently through all towns and villages , which leads us to the necessity of creating more efficient data loggers that can support unfavorable weather conditions for long periods which can help determine weather conditions after any sudden corpse discovery. It is important also to mention the necessity of developing the meteorological stations by improving the quality and efficiency of equipment which yields to better results and gives more accurate and reliable data.

Forensic entomology faces seasons’ challenges: not all insects are present or fully active during all seasons. Calliphora vicina, a bluebottle blowfly, grows all year round but in winter its development slows right down. While it remains alive, it becomes inactive at temperatures below 1C. Dorothy E. Gennard wrote in her book :”Greenberg (1990) stated that calliphorids do not fly in the rain. Digby (1958) examined the effects of wind speed on the ability of Calliphora vicina (then known as Calliphora erythrocephala) to fly. He recorded an optimal wind speed for flight of 0.7 metres/second and suggested that speeds greater than this inhibited the ability of Calliphora vicina to fly. Temperatures above 30C and below 12C are also known to inhibit blowfly activities. This fact should be taken into consideration when interpreting the conditions at a crime scene, as the blowflies may not have been in a position to fly to find a body where the temperatures have not been favorable. Calliphora vicina shows a single (unimodal) peak of daily activity in the cooler months, when the flies are most active around midday. In contrast, in the warmer months, this species is active at two periods in the day, with least activity during the hottest part of the day (Erzinçlioglu, 1996). Changes in peaks of seasonal activity will also be related ˘ to seasonal peaks in fly populations. Johnson and Esser (2000) suggest that in the tropics, blowfly population peaks are synchronized with the early and late stages of the rainy season, when relative humidities and temperatures are high but rainfall is not at its maximum. Thus, the influence of the seasons may affect the interpretation of when the eggs were laid on a corpse. In general, blowflies overwinter in soil as third instar larvae. Lucilia spp. have a maternally-induced diapause in the third instar; this differs in Calliphora vicina, in which populations only undergo diapause if they are northern, since the weather in the north can drop below freezing. Both Calliphora vicina and Calliphora vomitoria tolerate a certain degree of supercooling. Calliphora vicina has a lower freezing threshold; the egg stage is particularly cold-resistant (Block et al., 1990). Survival strategies of particular species and the location of the corpse should therefore be considered when interpreting the post mortem interval from species which are present on a body early in the year. “ Climatic change may be playing a role in altering the distribution of Calliphoridae and be responsible for changes in the range of some species. Phormia regina is another specie whose variation in the length of the life cycle occurred at higher temperatures (35 − 45C), when adults failed to emerge. Researchers also found a variation in the length of the life cycle when cultures were kept at a constant temperature of 40C or at 10C (this observation is interesting as, in Phormia regina, activity is thought to be inhibited when monthly temperatures have an average of below 10C. Thus, having insects that change activity rate during seasons affects investigations. Forensic entomologists are no longer capable of taking usual insects as specimen, therefore the discovery and study of other possible species relative to each season is a must. Labs should be well equipped to conduct studies and experiments in collaboration with entomologists in order to provide information on new species that might replace others for investigations under certain climatic circumstances.

Total absence of insects due to freezing, burying or wrapping the body. Forensic entomologists might find altered species or even total exclusion leading to lack of evidence since altered species means altered development and this would cause a deficit in information regarding the crime. The body might be frozen, sealed in a tightly closed container, or buried very deeply. Low temperatures drive insects away and leave the body undecomposed. If the body is wrapped, it would be difficult for insect to reach it and lay their eggs on it. The development cycle of the specie would be interrupted and an analysis of this cycle would be impossible. Also, burying a body deeply causes certain types of species to leave it heading towards certain soil levels where conditions are favorable for their living. Since the conditions of murder or suicide are out of control, entomologists may find a big challenge dealing with these cases. Therefore, entomological evidence must be replaced by analysis of fabric wrapping the body or soil specimen interacting with the body…


Forensic entomology is a primary branch for crime investigations and no matter what challenges might face the experts in this field, governmental support remains essential in order to provide solutions and funding. The world is heading towards greater development and progress, therefore it is a need that forensic entomologists get the training they need along with replacement techniques and it is crucial for all scientists and labs to conduct experiments and studies that would be a gain not only for investigators but for the entire nation in general. New information with new tools in hands of experts can assure a fast and easy way to justice in solving crimes and revealing all about murders and suicides.

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