What Is Forensic Entomology?

Forensic entomology, also known as Medicocriminal Entomology, is the use of insects to aid legal investigations. The vast field of forensic entomology is usually broken down into three main areas: medicolegal, urban, and stored product pests.

The medicolegal area focuses on the necrophagous feeding insects that infest human remains. The urban section looks at insects that affect man and the immediate environment. And stored product pests are insects found in foodstuffs, which may be used during proceedings involving food contamination.

Forensic entomology is becoming ever more widely used, and entomologists are being called upon more and more to apply their insect knowledge to criminal and civil investigations. This field of forensics has many uses. Forensic entomology is more commonly used to determine time of death of a person, but it is also used in the investigation of automobile accidents (as it is believed bee and wasp stings are responsible for so many road accidents) and also in blood spatter analysis (insects can often move through blood, leaving trails at crime scenes).

History Of Forensic Entomology

It is widely believed that forensic entomology is a fairly new method in the field of forensics, but this is not true.

In 1235 AD Sung T'zu, a Chinese '"death investigator", wrote a book, "The Washing Away Of Wrongs". In this book was the first recorded mediocriminal entomology case. A murder occured in a Chinese village, and the local "death investigator" was sent to solve the crime. After interviewing several people, he had the villagers bring their sickles out and lay them down. Sung T'zu waited for hours, the villagers curiously wondering what he was doing. Soon flies appeared and were attracted to one particular sickle. Sung T'zu concluded that this sickle probably had the remains of human tissue on it, which had attracted the flies.

The next observations to be made were in France and Germany during mass exhumations in the late 1880's, by Reinhard and Hofmann. Then in 1894 Mégnin wrote a popular book, and after this the concept of forensic entomology quickly spread to the US and Canada. From the 1960s to the 1980s Leclecq and Nuorteva were mainly responsible for maintaining the method in Europe in case work. Since then research in the US, Russia and Canada has been carried out, leading to entomology now being used routinely in investigations.

Now forensic entomology is commonly used in criminal investigations, and entomologists are more often being called in to use their knowledge to assist.

Life Cycles

There are roughly 700,000 recorded species of insects living on the Earth, each one different. However most insects important to a forensic entomologist undergo a complete "holometabolous" development, and by studying this, much can be learned that is useful to an investigation.

The first stage is the egg stage which hatches into larval form, with the exception of a few insects that deposit living larvae. When in the larval form, it then undergoes an incremental growth, shedding any outer skin that has become too small. The larva then reaches the inactive pupal stage. The pupa is the hardened outer skin, inside of which the adult develops until it is ready to leave the pupa.

Metamorphosis

Insects develop by one of three types of metamorphosis.

Ametabolism - This is more or less no change. The young emerge from the egg looking like a small adult. Over time the insect increases in size and soon reaches sexual maturity. This is the life cycle of insects known as primitive insects, such as the Thysanura. These insects may continue to grow even after reaching adulthood.

Hemimetabolism - There is more of a gradual change here, although the young still do have the same form as adults. There is a development of wings through the instars and often changes in colour and shape. This form of metamorphosis has three distinct stages; Egg, Nymph and Adult.

Holometabolism - This type of metamorphosis has four distinct stages; Egg, Larva, Pupa and Adult. The larva is usually a grub, caterpillar or maggot, bearing little resemblance to the adult. The young actively feeds and grows. The pupa tends to be an inactive stage, during which the insect reconstructs itself into adult form. Insects that have holometabolism include flies, beetles, wasps and butterflies.

Common Insects

There are currently approximately 700,000 different species of insects discovered, and it is estimated that there are another 1 million species yet to be discovered. At any scene with a human or animal corpse, the first to the scene is almost always the insects. A wide variety of insects are attracted to these scenes, and below are some of the most common.

Acari

Acari, also known as mites, are small organisms usually sized less that 1mm. Mites occur in the soil under bodies during the later stages of decomposition. Most mites are transported to the body by other insects, such as beetles or flies. Most species of mites can be found in the soil or seepage area under the body.

Aranea

Aranea, or spiders, are predators on insects that occur on corpses. They have limited or no value in the estimation of post-mortem interval.

Diptera

Diptera is the collective group of insects with one pair of wings. There are approximately 100,000 species known, and many more undiscovered. In this group we may find members of the carrion fauna. Below are some of the members of the diptera group.

Trichoceridae

Trichoceridae are more commonly called winter-gnats, because the species is more common in the winter months, though they do occur at lower frequencies throughout the rest of the year. The adults share the appearance of small crane-flies. The larvae, which are saprophagous, feed on decaying material, and are an important part of the carrion fauna during winter, when the blowfly fauna are missing.

Stratiomydae

Stratiomydae are the larvae of Hermetia illucens, and feed on human remains and human excrement. This species usually occur quite late in the process of decomposition.

Phoridae

The Phoridae are a large fly family containing around 3000 different species. They are sized between 0.75mm to 8mm, and are dull black, brown or yellowish in colour, having a hump-backed appearance. Due to their erratic, active manner, they have been aptly nicknames scuttle-flies. These flies breed in a variety of decaying organic material, as well as some parasites and fungi. One common species of the Phoridae is the coffin fly, due to its association with coffined bodies. The stages between the egg to adult of the coffin-fly does take a considerable time, as the temperature variation is slight.

Syrphidae

Syrphidaeare also known as hover flies, and are often camouflaged as bees or wasps. Amongst the larvae of this species is the famous rat-tailed maggot, and these occur in filthy water and sometimes dead bodies.

Dryomyzidae

The Dryomyzidae is a small group of fairly rare flies. They tend to be found in moist wood, and their larvae occur in decomposing organic material.

Coelopidae

The Coelopidae are s mall to medium in size, and tend to be black or dark brown in colour. The body and legs are bristly, and have the dorsum of the thorax flattened. The Coelopidae occur along the seashore, and are plentiful where seaweed has washed up.

Heleomyzidae

Heleomyzidae is a large group of flies sized small to medium, and are usually brownish colour. They are often found in moist areas, the larvae being found more in decaying plant or animal matter.

Sepsidae

These flies occur in large groups around decaying material and excrement, which is where the larvae develops. This species feed on dead human bodies in the time of caseic fermentation. The eggs of Sepsidae have a long respiratory horn, usually longer than the egg itself.

Piohilidae

The Phiohilidae are dark flies, their larvae often found on dead bodies that have been lying for a while. This specie is also known as the Cheese-skipper, because the larvae jumps when disturbed. These flies have also been known to infest cheese and bacon.

Ephydridae

This is a large group with several common species. They are small in size, and tend to be found in moist places, such as marshes, shores of ponds and streams, and seashore.

Drosophilidae

The Drosphilidae are more commonly known as fruitflies. Small in size, they are grey, yellow or brown in colour with brightly coloured eyes. The larvae feeds on decaying vegetables and fungi. Some do occur on dead humans, but most likely to be feeding on fungi.

Calliphoridae

The Calliphoridae are the well-known bluebottles and greenbottles. There is many species of blowflies, each different. Some prefer light areas whereas some prefer the shade, some are urban and some are rural.

Muscidae

Among this large family is the housefly. They occur in houses and are one of the most common species in the world. If the temperature is warm they can complete development in 14 days. Their eggs are laid in decomposing material, especially dead bodies.

Coleoptera

Coleoptera are beetles, and the various groups in this family occur in different stages of decomposition. Below are some of the most common species in this family.

Staphylinidae

Also known as rove-beetles, they may arrive just a few hours after death, remaining active throughout the decomposition process. The adult larvae will feed on eggs and even the larvae of other species.

Dermestidae

These are common beetles found in the later stages of decomposition. Larvae of these do not occur before the body is dry. The adults and larvae will feed on hairs, dry skin and other dry dead organic material. This is a common stored product pest in homes and museums.

Histeridae

The members of this family have short elytra. Histeridae occurs wherever there is decay and putrefaction. They have often been found on the bloated, and early parts of the dry stage. They tend to be concealed under the corpse in the day, becoming active at night.

Different insects will arrive at the scene of a decaying body at different times. During the first three days after death, around the time the Proteins and carbohydrates in a body are beginning to break down, the first to arrive at the scene will be blowflies, such as bluebottles. Over the following three days as the body starts to decay and the abdomen inflates, fly larvae and beetles will appear. Between days 8 and 18 as decomposition truly sets in, flies, beetles, ants and cockroaches will be present. Through days 19 to 30 the body enters the ‘post-decay’ stage, finally attracting beetles and mites.

Death Scene Protocol

At a death scene at which insects or anthropods are present, it is important that the procedure is followed correctly. Usually we would start by noting any scene and weather observations. Some insects would be collected from the body at the scene, and some would be collected after the body has been removed. Any collected specimens would then be shipped to a forensic entomologist for analysis.

When observing the scene one should note the location of the body, as in the habitat in general. Included in these observations would be any vegetation, sun or shade conditions and any open doors or windows, if indoors. As well as noting what stages any insects found are in, it should also be noticed where on the body the insects are infesting. The weather and any climatological data should also be noted. The air temperature is taken with a thermometer in the shade, but the thermometer must never be exposed to direct sunlight. Also noted are the maggot mass temperature, the ground temperature, the temperature between the body and ground, and also daily weather temperature and rainfall.

When the time comes to collect insects, adult flies and beetles should be the first to be collected, as they are fast moving and after being disturbed can leave the crime scene fairly quickly. The collected flies are immobilized with ethyl acetate, and then transferred to a vial of 75% ethyl alcohol. The beetles can be placed straight in the vial. Next larval specimens are to be collected. First any eggs should be looked for carefully, as they can be difficult to spot. The larvae are then collected, stored the same way as flies and beetles, but sometimes boiled for preservation.

Once the body has been removed from the scene, more insects should be collected from the area under and around where the body was. The same steps as described above should be carried out. Soil samples should also be collected at this time. The specimens are then to be shipped correctly with sufficient food and air.

Equipment

A forensic entomologist should always carry the correct collection equipment, and also have other required equipment easily available to them.

Nets:

Aquatic Net Bag – Used to collect insects from water or similar.

Insect Net Bag – Used to collect other flying insects.

Forceps – These ‘feather-touch’ forceps are used to collect insects without damaging them.

Collection Containers – These are used for collecting and shipping specimens in.

Vials – Vials are used to place collected specimens at the scene. Suitable only for short-term use.

Killing Jars – Jars in which insects must be killed.

Field Spotlights – Often used to cast light over particular areas.

Uses Of Forensic Entomology

-Estimating Time Of Death-

Probably the most common use for forensic entomology is estimating the time of death. Once a body begins to decompose, many different insects are attracted by the smell of decay, and through these insects’ life cycles we can work out an estimate of time since death.

The first to appear at the scene is usually the Diptera, especially blowflies and fleshflies. The females will lay their eggs around the orifices, such as the mouth and nose. If the body has wounds, they will also lay they eggs there. The fleshflies do not lay eggs, and just deposits larvae. The eggs will soon hatch into larvae, which will feed on the dead tissue, growing at a fast rate. It soon malts, reaching the second larval instar. It will once again eat more, and then reach the third instar. When the larvae are fully-grown it reaches the pre-pupal stage, then malts into pupae. Usually it takes one to two weeks to move from the egg stage to the pupae stage, depending on the individual species and the general environment.

By studying these stages, we can often estimate the time since death. The egg stage will last about one day, the larvae stage can last up to around the fifth day, the pre-pupal stage occurs on days 8-12, and the pupa are seen 18-24 days after oviposition.

-Finding Cause Of Death-

Sometimes any insects found at a scene can shed some light on what happened when the victim died. Every year many deaths are caused by bee and wasp stings, and the presence of these at a scene can suggest the victim was stung.

Eventually at a scene of death it will become impossible to sample urine, blood and stomach contents. However if there are maggots present, maggots that have fed on the remains, they will have ingested the tissue. We can take the maggots and may be able to extract useful samples from them, such as poisons. Some chemicals and poisons ingested by maggots may influence life cycles.

-Movement Of The Body-

By looking at the fauna at the body, a forensic entomologist can estimate how long a body has been lying there by taking soil samples from under the body. By analysing this soil it is possible to estimate the post-mortem interval, and maybe whether or not the body has been moved.

If a body is found in an environment where blowflies could not access, yet there are blowflies present, this also suggests the body has been moved.