Unit 5: Forensic Entomology

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Unit 5: Forensic Entomology

By Kate Harrington

Open Ended

What is Forensic Entomology?

The Postmaster and the Ferry Skipper

In September of 1956, a postmaster was stabbed to death on a ferry in Hungary. The ferry skipper was arrested for the murder. He had arrived at work at about 6 p.m., several hours before the body was found. The autopsy included the collection of yellow fly eggs and hatched larvae that were about 1 to 2 mm in length. The skipper was tried and convicted of the crime. Although he was sentenced to life in prison, he continued to proclaim his innocence.

The Postmaster and the Ferry Skipper

Eight years later, in 1964, the case was reopened. A forensic entomologist from Budapest’s Natural History Museum argued that insect evidence proved the skipper was innocent. The entomologist testified that the eggs on the postmaster’s remains were from a species of fly that couldn’t have been active at the time of the murder because it was too cold. Furthermore, newly hatched larvae were present during the autopsy. This indicated that the eggs must have been laid before the skipper even arrived at work at 6 p.m. the previous day, and the death must have occurred before then. Therefore, the ferry skipper could not have committed the murder. The skipper’s sentence was overturned, and he was released.

The Postmaster and the Ferry Skipper

This case shows just how important forensic entomology can be in a crime investigation. Without the sharp eye of the entomologist, the ferry skipper would have spent his life in prison for a crime he didn’t commit. Forensic entomologists use their expert knowledge to investigate insect evidence surrounding crimes. This evidence can often be vital to reconstructing a crime, finding a suspect, or, as in the case above, restoring justice.

The Life Cycle of a Yellow Fly (Tabanidae)

​Entomology

Entomology is the scientific study of insects. Whether you like them or hate them, insects are an important part of global biodiversity. They inhabit almost every environment on Earth and account for the majority of known species. Around 1.3 million species of organisms have been identified and described today. Of these, about two-thirds (700,000 species) are insects. Scientists estimate that there are between six and ten million species of insects present today, most of which have not been identified or described yet.

Open Ended

What would an Forensic entomologists be called to do?

​Entomology

Forensic entomology is the study of insects, including insect behavior, in situations related to crime. Forensic entomology draws upon research produced by entomologists about insect life, biology, and behavior. Forensic entomologists may also examine organisms closely related to insects if those organisms can provide evidence about a crime. There are three specialized areas within forensic entomology: medical/legal, urban, and stored products. The medical/legal area of forensic entomology is concerned with insects in connection with human remains. This includes studying the presence of insects on a body and studying how insects contribute to accidents (for example, a car accident caused by a driver trying to kill a bee in the car).

​Entomology

The urban area is concerned with insects that interact with humans and their living environments. Here, forensic entomologists might be called upon to help with civil or criminal cases of insect infestation, bites, and insects feeding on various remains. Finally, forensic entomologists who study stored products examine insects that infest food. They may testify in food contamination cases. In this unit, we will be focusing primarily on the medical/legal area of forensic entomology, although other areas may also overlap with criminal investigations.

​Forensic entomologists may be able to determine:

Has the body been moved?

Wounds and their position

​Presence of drugs in the body

Was the suspect at the scene of the crime?

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Has the body been moved?

In some cases, a body is moved after death from the scene of the killing to a hiding place. Some of the insects on the body may be native to the first habitat but not the second.

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Wounds and their position

Has the body been moved?

Once a body begins to decompose, it can be harder to examine wounds. Insects can provide clues about the presence and position of wounds as they typically colonize remains in a certain pattern, beginning in the facial orifices. If there are wounds, though, insects will favor those areas instead. So if maggot activity is not centered at the orifices, they will be probably be at the site of a wound.

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Wounds and their position

Has the body been moved?

Once a body begins to decompose, it can be harder to examine wounds. Insects can provide clues about the presence and position of wounds as they typically colonize remains in a certain pattern, beginning in the facial orifices. If there are wounds, though, insects will favor those areas instead. So if maggot activity is not centered at the orifices, they will be probably be at the site of a wound.

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Presence of drugs in the body

If a body is decomposed, there may not be enough flesh left to determine whether drugs are present, but since maggots bioaccumulate drugs, they can be examined to discover whether drugs are present (and what type).

​​bi·o·ac·cu·mu·late

/ˌbīōəˈkyo͞omyəlāt/

verb

1. (of a substance) become concentrated inside the bodies of living things.

Was a suspect at the scene of the crime?

A suspect can be linked to the scene of a crime if an insect attaches itself to plant matter. The plant matter can then be transferred to the suspect during the crime.

Blowflies and Human Remains

Forensic entomologists often look for the presence of flies when examining human remains. Blowflies are often the first type of insect to find a dead body and begin interacting with it. This is because blowflies can smell even the faint odor of a decaying organism from more than a mile away. Since these insects also have a fairly predictable life cycle, they can reliably indicate the amount of time that has passed since death.

Blowflies and Human Remains

Blowflies are typically recognized by their metallic green or blue coloring. The name blowfly comes from the term “fly blown,” which was an older English term for meat that had fly eggs laid on it. There are over 1,000 different species of blowflies worldwide.

Let’s take a closer look at the life cycle of the blowfly and how it can help forensic entomologists.

It's Florida and you have found a body....

0 - 60 Seconds...

Adult blowflies will smell the beginning of decay in the body. They move in and begin feeding on any proteins available, including blood, sweat, and tissues.​

It's Florida and you have found a body....

0 - 60 minutes...

Adult blowflies will smell the beginning of decay in the body. They move in and begin feeding on any proteins available, including blood, sweat, and tissues.​

It's Florida and you have found a body....

1 Day...

The blowfly eggs begin to hatch into maggots. The blowfly maggots are about 1/5 of an inch long, and they have a protective outer layer on their bodies. The maggots begin to feed on the body as soon as they are hatched. As they feed and grow, the maggots outgrow their outer layers and shed them. Forensic entomologists are often able to find these shed outer layers a day after death.

It's Florida and you have found a body....

4 to 5 Days...

The maggots continue to feed and they reach their largest size (about 2/3 of an inch). The large number of maggots can raise the temperature of the surrounding body by up to 50° F.

It's Florida and you have found a body....

8 to 12 Days...

This stage is known as the wandering or post-feeding stage. The maggots stop eating and shrink a little bit in size. The maggots begin to leave the body for nearby areas, including rocks or vegetation.

It's Florida and you have found a body....

Adults

Eventually an adult blowfly emerges from the pupa. At first, the blowfly has a soft body and its wings are still wrinkled and collapsed. Within a few hours, the wings expand and the blowfly resembles a typical blowfly adult. Within about 5 to 18 days, the adult blowfly will start reproducing and the female will look for another dead body to lay her eggs on.

It's Florida and you have found a body....

Adults

Eventually an adult blowfly emerges from the pupa. At first, the blowfly has a soft body and its wings are still wrinkled and collapsed. Within a few hours, the wings expand and the blowfly resembles a typical blowfly adult. Within about 5 to 18 days, the adult blowfly will start reproducing and the female will look for another dead body to lay her eggs on.

Multiple Choice

What factors can affect the speed of the blowflies' growth?

• location of the body, temperture, and age of the victum at time of death

• location of the body and temperture

• the age at the time of death and the cause of death

PMI

A number of factors can influence estimations of post-mortem interval (PMI), or time since a person died. One important factor is temperature. Temperature can affect the blowfly life cycle. For example, if the weather is around 70°F when the blowflies begin laying eggs, but the temperature then drops, the cycle will be delayed. Blowfly eggs may develop slowly in cooler weather, or development may stop altogether until the weather warms up. Cool weather can delay the life cycle of the blowfly for hours or even days. Another factor to consider in determining time of death is exposure to insects. For example, if a body is stored in a closed space after death and exposed to insects only later, time of death estimates based only on insect activity will be off.

Necrophagous insects

Although blowflies are common visitors on a dead body, they are not the only insects found. Other insects can also be useful in determining post-mortem interval. A general sequence of insects appear on and near human remains. Necrophagous insects (insects that feed on decomposing flesh) are the first insects to appear. Blowflies are an example of a necrophagous insect.

Necrophagous insects

After the arrival of the first necrophagous insects, predator insects begin to appear. These insects feed on necrophagous insects. The predator insects may include beetles as well as other types of insects that feed not only on the decomposing flesh but also on the maggots and other insects already on the body. The third set of insects that appear are omnivore insects. These insects feed on the other insects, the body, and any other available edible material, including plants. Both wasps and ants are examples of omnivore insects that may appear on human remains

Necrophagous insects

Finally, other organisms that are indigenous to the area will come into contact with the body. Generally, these organisms will not seek out human remains for food, but they may come into contact with it as they move through the area. Spiders are one example of an organism that might be found on or near human remains.

Most Common Necrophagous Insects

• Flies^[1]

• Beetles

• Moths

• Mites

• Bees

• Wasps

• Ants

• Spiders

Collecting and Handling Samples

Forensic entomologists rely on receiving accurate samples of the insects that appear in and around the body. Accurate samples and information help forensic entomologists make their best estimates about post-mortem interval. Since the collection of insects may disturb the human remains, forensic entomologists must work closely with investigators to minimize disturbance while gathering the most information possible.

Open Ended

What are the first steps we should take when we enter a crime scene?

​Entering a Crime Scene

Before any insects are collected, other relevant information is observed and recorded. The body’s location is an important piece of information for forensic entomologists. Vegetation around the body can influence which insects are found. collected from before the person’s disappearance to several days after the victim was discovered.

​Entering a Crime Scene

In addition, forensic entomologists record whether the body is in the shade or the sun, since this may influence the timing of the insect life cycles. Forensic entomologists also record the temperature of the air, the body, and the maggot mass if it is present (a thermometer is placed into the center of the group of maggots). They collect weather data for the location, including high and low temperatures as well as precipitation. If the body is suspected to be a particular missing person, data will be collected from before the person’s disappearance to several days after the victim was discovered.

Multiple Choice

What are some methods for collecting evidence?

• notes, photograpsh, video recording, drawings taken by a forensic professional

• Photographs and video only

• notes, photographs, video recordings, drawings

• Only evidence taken by licensed professionals may be used in the investigation.

​At the Lab

When the insect samples arrive at the laboratory, forensic entomologists examine them along with any other information provided by investigators. Forensic entomologists will first try to determine which types of insects were present at the scene. Identifying species is an important task, as it provides forensic entomologists with background information about average growth patterns and life cycles. It can also be important to identify species if a body has been moved. In some cases, insects may be present on the body that are not native to the area or that are not common in a particular habitat.

What Information Can Be Gained

toxicology information

time of death​

Multiple Choice

Danielle is a forensic entomologist working at the scene of a murder with a crime scene investigator. Which concern should she prioritize over all others?

• comfirming the species of necrophagus fly

• collecting eggs from within the body

• measuring the the temperture of the maggot's mass

• collecting accurate samples

​Correct Answer

Because inaccurate or contaminated samples could lead Danielle to draw inaccurate conclusions from the collected evidence, collecting samples with the utmost care for accuracy is always her top priority.

Multiple Choice

Because inaccurate or contaminated samples could lead Danielle to draw inaccurate conclusions from the collected evidence, collecting samples with the utmost care for accuracy is always her top priority.

• stained it with chemicals

• tested it genetic code

• placed it under a microscope

• weighted and measured it

Correct Answer

Tested it Genetic Code - Using a PCR analysis, Jackie can identify or confirm the species of fly collected from the unidentified body.