Week 4 - Entomology

What is entomology

The study of insects. Forensic entomologists use insects to provide info about a crime and this role can be as informative as biological evidence

When is entomology particularly relevant

48-80 hours after an event, when the body’s physiological changes are no longer readily interpretable by forensic pathologists. At this point the body is decomposed and the smells and fluids emanating from it will attract insects to be used as a food source, shelter, or a site to reproduce/lay eggs

How are insects predictable

All respond to opportunities to gain food, shelter, a place to reproduce and lay eggs, and a place to develop through their life cycle. Because of their predictability, forensic entomologists can use this to their advantage to establish when and where a crime took place, how much time has passed since the crime, and even time of death

Things to consider about what insects can tell us

• Types of insects - different insects are expected to display different behaviours

• Environment - different insects are present in different places and may act differently depending on the environment they are in

• Season - some insects are only present at certain times of the year

How can insects help establish when and where

• Some insects only found in specific areas

• Some insects only active at night or during the day

How can insects help establish time of death

Some insects lay eggs in dead bodies, so knowing the life cycles of different insects and the stages of decomposition when different insects populate dead bodies can determine time since death, or the length of time the body has been there, if it has been moved

What insects will arrive to a dead body at what times

• Airborne insects like flies will always be the first to arrive as they can get there first due to flying

• Beetles tend to arrive as the body decomposes, usually during stage 5 putrifaction

Differences in insects’ attraction to dead bodies

• Some are attracted to newly dead bodies, others will only arrive 3-6 months after death

• Some scavenge dead flesh from bodies to use as a food source, whereas others use the body as shelter and a site to reproduce/lay eggs

• Some aren’t attracted to dead bodies at all, such as fleas and mosquitos who host on live bodies for blood as food sources

Which part of a dead body to insects go first

Cavaties in the body or orifices

What are body farms (Human Taphonomy Facility HTF)

Sealed off areas where donated dead bodies are left in the open environment, and their decomposition is monitored to understand how fast/slow the body decomposes, what types of insects arrive at what times and why, and what clues that provides about the crime

How are blood sucking insects useful

Forensic scientists can extract blood consumed by blood-sucking insects, and this can be used to place someone at the scene of a crime, supported by evidence of bite marks

DNA/toxicology and insects

• Date rape drug can potentially be extracted from larvae to support sexual assault

• DNA and drugs can be extracted from the gut of some insects, may also get DNA from larvae if they are eating the decomposing body they were laid in

• Other drugs have been found in larvae - e.g. opiates, anti-depressants

What can the presence/absence of insects on a body tell us

• Time and place

• Movement or journey a body has made

• Storage of a body - e.g. larvae discovered in December would be unusual, indicates body stored since at least September when insects would last be active and reproducing

How can insects be used as evidence in animal and human abuse cases

• Flies can lay eggs in untreated wounds, bedsores

• Flies are attracted to unchanged nappies or incontinence pads in neglected babies and elderly or disabled people

How can insects offer false leads

Insects can walk through bloodstains and leave bloodstained droppings at crime scenes, which can cause confusion

How can insects cause crime

Bee and wasp stings can cause car accidents, and police may call forensic entomologists to confirm this as a cause, e.g. some people have severe allergies to bee/wasp stings which may cause them to pass out while driving and cause a crash. If the sting was fresh, this can be consolidated as a cause

Stages of decomposition

1. Pallor mortis

2. Algor mortis

3. Livor mortis

4. Rigor mortis - when the body goes stiff

5. Putrefaction - when body breaks down and almost liquifies 

Changes in the body during decomposition

• Core body temperature drops gradually

• Chemical changes - potassium levels in vitreous fluid (eye) creates a cloudy appearance (glazed over eyes)

• Hypostatis - blood settles in lower parts of body and begins to pool (depending on how positioned), within first 30/45 mins

• Body begins to stiffen (rigor mortis) anywhere from 20-120 mins and is fixed for 10-12 hours

Stages of decomposition in water

1. Fresh stage

2. Bloated stage

3. Active decay stage

4. Post decay stage

5. Skeletonization

How does decomposition differ

Based on whether the body is decomposing on land, in water, or at different altitudes

Why are the stages of decomposition not definitive

• Not always easily separable stages

• Varies across individual bodies

• Whether left in the open, humid vs. dry, presence/absence of insects, water

How can insects make a body decompose faster

By eating the body’s tissue, or if there are a lot of insects on the body, by increasing the temperature and accelerating decomposition

What forensic entomologists use to determine time of death

• Life cycle of species

• Sequencing and presence of species

• Mitigating factors, e.g. temperature, environmental conditions

Blowfly

• Similar to a house fly but larger

• Attracted to rotting animal carcasses as food source

• Larvae go through several stages that can be identified

• Within a stage, age can be determined by length

• Age of pupae determined by darkening of colour

Blowfly cycle

Eggs → larvae (instar) → pupae → flies

Potential problems

• Reproduction cycles depend on region of world, time of year, temperature

• If body is indoors, arrival of insects will be slower

• Some insects will pause their development, e.g. unreasonable weather, a storm, insects will go to ground to seek shelter

• Maggot feeding masses may raise temperature and reduce development times

• Incorrect collection, storage and lab processing of larvae may lead to over/under estimation of time since death

What can the presence of insecticide tell us

If large amounts of insecticide is used on a certain crop we might be able to tell if a person was killed in that environment as there wouldn’t be a large presence of insects on the body