Forensic entomology | The crime scene

Summary

This script delves into the crucial role of forensic entomology in crime scene investigations. It explains how entomologists assist pathologists by studying insects attracted to a body to determine the post-mortem interval. The life cycle of blowflies, their rapid response to decomposition, and their preferred egg-laying sites are highlighted. The script also explores the challenges faced, such as the impact of a body being concealed in a suitcase, demonstrating the insects' persistence in locating and accessing a body for feeding and reproduction.

Takeaways

• 🐛 Insects are commonly found at crime scenes and can provide crucial evidence, even if they are not initially visible.
• 🕵️‍♂️ The role of an entomologist is to assist pathologists by studying the insects on and around a body to determine the post-mortem interval.
• 🕒 The minimum post-mortem interval is the time elapsed since the first insects colonized the body after death, which can be within 12 to 24 hours in summer in the UK.
• 🔍 Forensic entomologists focus on recovering insect evidence from the crime scene and may continue their analysis in a post-mortem setting.
• 🦋 Blowflies are considered the gold standard forensic indicators due to their rapid response to decomposition and their life cycle that closely follows death.
• 🥚 Female blowflies lay up to 200 eggs on a decomposing body, which is an ideal substrate for their development.
• 🐛 The life cycle of blowflies includes egg, larva, and adult stages, with the larvae feeding on the body and undergoing several molts before pupating.
• 📈 The development of blowfly larvae can be tracked by observing temperature changes, as seen in the example of a stillborn piglet.
• 🌡 The choice of egg-laying sites by blowflies is influenced by factors such as humidity, with body orifices being preferred due to higher moisture levels.
• 🧳 Even when a body is concealed in a suitcase, flies can still detect it, oviposit through the zip, and the larvae can enter and feed on the body.
• 🔎 Environmental and human factors can complicate forensic entomology investigations, making it challenging to analyze insect evidence.

Q & A

What role do insects play in a crime scene?

Insects are likely to be involved in a crime scene either accidentally or because they have moved there in response to elements of the crime scene. They can provide crucial evidence, particularly in determining the post-mortem interval.

How does an entomologist assist a pathologist in a forensic investigation?

An entomologist helps a pathologist by examining the insects feeding on and around the body, which can provide a minimum post-mortem interval, indicating the time since the first insects colonized the body after death.

What is the typical time frame for insect colonization on a body outdoors during summer months in the UK?

In the UK, during the summer months, a body outdoors is usually colonized by insects within 12 to 24 hours.

Why is it important for forensic entomologists to recover insects from a crime scene?

Forensic entomologists need to recover insects not only from the body but also those that have dispersed away after feeding, as they can provide valuable evidence about the timing and circumstances of the crime.

What are the 'gold standard' forensic indicators in entomology?

Blowflies are considered the 'gold standard' forensic indicators because they are the first to arrive at a decomposing body and have a strong sense of smell to locate it quickly.

How many eggs does a female blowfly typically lay on a human body?

A female blowfly will lay between 150 to 200 eggs on a suitable substrate, such as a human body.

What is the life cycle of a blowfly from egg to adult?

The life cycle of a blowfly includes the egg stage, which hatches into first-stage larvae, then moults into the second stage maggot, followed by the third stage maggot, and finally, after pupation, emerges as an adult fly within about 10 days in the UK summer.

How do blowflies locate a decomposing body?

Blowflies respond to the odours of decomposition and navigate upwind through the odour plume until they arrive at the scene, using visual cues to land on and explore the body for suitable egg-laying sites.

Why are blowflies particularly attracted to body orifices for egg-laying?

Eggs are susceptible to desiccation, so blowflies choose areas with higher humidity, such as body orifices, which also provide the larvae with access to internal tissues that are less protected from their enzyme activity.

What impact does placing a body in a suitcase have on insect colonization?

Placing a body in a suitcase can delay the arrival of flies by one to three days or more, depending on the temperature, but they will eventually find the body, oviposit through the zip, and the larvae will enter and feed on the body.

How do forensic entomologists use temperature changes to track insect activity on a body?

Forensic entomologists can take a series of images over time to observe temperature hotspots, which indicate areas of active larval feeding, helping to track the progression of insect colonization and decomposition.

Outlines

00:00

🐛 The Role of Insects in Forensic Science

This paragraph discusses the prevalence of insects in nature and their potential involvement in crime scenes. It explains the role of an entomologist in assisting pathologists to determine the post-mortem interval by studying insects that feed on a body. The focus is on the life cycle of blowflies, which are the first to colonize a body and serve as key forensic indicators. The paragraph details the rapid response of blowflies to a decomposing body, their egg-laying habits, and the development stages of their larvae. It also touches on the insects' behavior post-feeding, their tendency to disperse, and the forensic significance of their colonization patterns, especially around the body orifices.

05:05

🔍 The Impact of Concealment on Insect Colonization

The second paragraph explores the impact of concealing a body, such as in a suitcase, on the ability of insects, particularly flies, to locate and colonize it. It describes an experiment using pig heads as surrogate bodies to demonstrate that flies can still find a concealed body, albeit with a delay depending on temperature. The paragraph explains how flies oviposit through the zip of a suitcase and how larvae can enter and feed on the concealed body. It also discusses the challenges faced by forensic entomologists in such scenarios, including the insects' ability to exit the suitcase through various openings, emphasizing the complexity of environmental and human factors in forensic investigations.

Keywords

💡Insects

Insects are a class of invertebrates with exoskeletons and three pairs of jointed legs. In the script, they are highlighted as ubiquitous in nature and often involved in crime scenes, either accidentally or due to their attraction to elements of the scene. The role of insects in forensic science is to provide evidence that can help determine the post-mortem interval.

💡Post-mortem interval

Post-mortem interval refers to the time elapsed since death. It is a critical concept in the script as it is the period the entomologist and pathologist aim to determine. The entomologist specifically looks at the insects' life stages on the body to establish a minimum post-mortem interval.

💡Entomologist

An entomologist is a scientist who studies insects. In the context of the video, the entomologist assists the pathologist by examining insects found on and around a body to help determine the time of death, making their role integral to forensic investigations.

💡Blowflies

Blowflies are a type of fly that are significant in forensic science due to their rapid response to decomposing bodies. The script describes them as the 'gold standard forensic indicators' because they are among the first to arrive at a scene and lay eggs, which helps in estimating the time of death.

💡Life cycle

The life cycle of an organism refers to the series of changes it undergoes from birth to reproduction. In the script, the life cycle of blowflies is detailed, from egg to larva to pupa and finally to adult, which is crucial for understanding the timing of their presence on a body.

💡Larvae

Larvae are the immature form of insects. In the context of the script, blowfly larvae hatch from eggs laid on a body and feed on it, growing through stages until they are ready to pupate. The development of larvae is a key indicator in determining the post-mortem interval.

💡Pupariam

A puparium is the hardened protective case that forms around the pupa of certain insects, such as blowflies, during their metamorphosis. In the script, it is mentioned as the stage where the larval tissues transform into an adult fly, which takes about 10 days in the UK summer.

💡Forensics

Forensics refers to the application of scientific methods and techniques to the investigation of crimes. In the script, forensic entomology is a specific branch that uses insects to provide evidence in criminal investigations, particularly in determining the time of death.

💡Decomposition

Decomposition is the process by which organic substances are broken down into simpler organic matter. In the script, the decomposition of a body is what initially attracts blowflies and other insects, which then become part of the forensic investigation.

💡Dispersal

Dispersal refers to the movement of organisms away from their place of origin. In the script, after feeding, insects disperse away from the body, which is an important behavior to consider when collecting forensic evidence, as some insects may have already left the scene.

💡Egg-laying site

An egg-laying site is a location chosen by an organism for the purpose of laying eggs. In the script, blowflies select sites with higher humidity, such as body orifices, to lay their eggs, ensuring the survival of the eggs and the larvae's access to internal tissues.

💡Metamorphosis

Metamorphosis is a biological process of transformation that some animals undergo after embryogenesis. In the script, the metamorphosis of blowfly larvae into adult flies is described, which is a remarkable process that is part of the insect's life cycle and relevant to forensic analysis.

💡Suitcase

In the script, a suitcase is used as an example of how even when a body is concealed, such as in a suitcase, insects like flies can still find it. The flies can oviposit through the zip, and the larvae can enter and feed on the body, demonstrating the persistence of insects in accessing decomposing bodies.

Highlights

Insects are likely to be involved in crime scenes, either accidentally or due to their attraction to elements of the scene.

Pathologists determine the post-mortem interval from the body's changes, while entomologists assist by studying insects associated with the body.

Entomologists determine a minimum post-mortem interval, the time since the first insects colonized the body after death.

In the UK, outdoor bodies are typically colonized by insects within 12 to 24 hours during summer months.

Forensic entomologists focus on recovering evidence from the crime scene and may continue their work in a post-mortem examination.

Insects that have fed on and dispersed from the body are of interest, as they may indicate the time and process of decomposition.

Blowflies are the gold standard forensic indicators, arriving quickly after death due to their keen sense of smell.

Blowflies lay 150 to 200 eggs on a decomposing body, which is an ideal substrate for their development.

Blowfly eggs hatch into first-stage larvae within 24 hours in UK summer conditions.

Larvae moult into second and third stage maggots, feeding for several days before dispersing to pupate.

The pupation process of blowflies involves metamorphosis from larva to adult within a rugby ball-shaped puparium.

The adult fly emerges after approximately 10 days in summer, completing the life cycle.

Blowflies navigate to a decomposition site upwind, using visual cues to find suitable egg-laying sites.

Eggs are laid in areas with higher humidity, such as body orifices, to protect against desiccation.

Larvae use body orifices to access internal tissues, which are more susceptible to their enzyme activity.

A time-lapse study shows temperature changes in a decomposing piglet, indicating larval feeding patterns.

Even when a body is hidden in a suitcase, flies can find it and lay eggs, with larvae entering through the zip.

Environmental and human factors can complicate forensic entomology investigations, presenting challenges for entomologists.

Transcripts

Insects are ubiquitous in nature

so they occur all around us all the time, even if we don’t see them

and therefore they're very likely to be involved in a crime scene

whether just accidentally or actually because they have moved there

in response to some element of the crime scene.

Looking at the body itself it will be the pathologist

who would look at the changes in the body and try to determine

from the body what the post-mortem interval is.

But as an entomologist I can help the pathologist

by looking, not at the body, but at the insects that are feeding on and around the body.

More precisely we are determining a minimum post-mortem interval,

that's basically the period that the first insects found the body after death.

Ordinarily in the summer months in the UK with a body outdoors

it would be colonised by insects within 12 or 24 hours.

At the crime scene the main thing is recovery of evidence

and I’ll do that at the scene and then go back to the post-mortem

and carry on there if necessary.

We're interested not just on the insects on the body

but on insects that have been feeding on the body

and may already have dispersed away,

because it makes good sense for these insects, once they finish feeding,

not to hang around on the body because some other scavenger

may come and consume them as well as the body,

so they tend to disperse away.

The gold standard forensic indicators are blowflies and these are the ones that come in first,

immediately after the body's dead and starts to decompose.

They have an incredible sense of smell

and will arrive very, very quickly after death.

The female fly will lay between 150 to 200 eggs on the suitable substrate,

and a human body is absolutely ideal for that.

Within about 24 hours in the UK summer

those eggs will hatch and they'll hatch into first stage larvae,

and these larvae are tiny, 1.5mm long.

Those larvae, though, are very hungry,

they will crawl into the recesses of the body and start feeding.

Within 24 hours they themselves moult into the second stage maggot

and then about another 24 hours later,

those will moult into the final, third stage maggot.

And that will feed for about three or four days.

When it's finished feeding it disperses away from the body

and looks for somewhere to pupate,

usually somewhere dark

It begins to harden itself and darken itself until it forms a rugby ball shaped pupariam,

and inside that pupa the larval tissues are reassembled

through metamorphosis into an adult fly,

it’s a quite remarkable process that amazes me even today.

After about 10 days in the UK summer the adult fly is now ready to emerge.

And so the life cycle continues.

When blowflies respond to the odours of decomposition

they tend to navigate their way upwind through the odour plume

until they arrive at the scene.

They will then use their visual cues to land on the body

and to move around and look for the most suitable egg-laying site.

Eggs are very susceptible to desiccation so they tend to choose areas

where the humidity is higher so that tends to be the body orifices,

the eyes, the nose, the mouth,

and the genital/anal orifices if those are exposed.

And of course the humidity is maintained in those environments

but it also affords the larvae the opportunity to crawl into the body

and feed on the internal tissues,

which are less well protected from the insects' enzyme activity

than the hard, tough, outer skin that normally covers our bodies.

So the focus of blowfly colonisation tends to be on the head orifices.

In this image just coming up here we have a stillborn piglet.

All you can see at the moment is the hotspot and you can see a fly that’s just landed on it there.

Surprisingly, although they’re coldblooded, flies themselves generate quite a bit of heat

through their flight activity and muscle activity.

The pig outline now is formed because we’ve adjusted the temperature range

and you can see there’s a couple of flies moving around there.

We know they’re not the first flies to have found this piglet

because that hotspot there is in fact where there is already a small maggot mass developing.

And what you can do actually is you can take a series of images over a timescale from,

in this case it was from day one to fourteen, so a couple of weeks period.

In the first six days or so, not a lot’s happening because it takes a while for these first flies

that have come in on day one to lay their eggs, for the eggs to hatch.

- this was during a winter period.

But on day six the temperature starts to go up in the mouth of the pig

and then over successive days that temperature hotspot moves down through the body of the piglet

as its being consumed basically by a larval mass

which is just rolling from the front end to the back end of the piglet.

And then after two weeks the piglet is now completely cold and empty.

All of the maggots have finished feeding and they’ve moved away.

So one of the accessibility issues we’ve been exploring at the museum just in the last few months

is the impact of putting a body in a suitcase.

Is it possible for flies to find a body in a suitcase?

And if so, how quickly?

Well, we found that using pig heads as surrogate bodies from a butchers shop,

just pop them into a normal, carry-on suitcase

and they delay the arrival of the flies by one to three days or more,

depending on the temperature.

However, the flies will arrive at the suitcase,

and they know that there’s a body in there.

And they will actually oviposit through the zip,

which most suitcases are sealed with these days.

The eggs will be laid into the suitcase

and in fact if they're just scattered around the zip

the larvae themselves when they hatch can crawl and enter the suitcase.

So even hiding a body in a suitcase won’t stop flies finding it

and once they’ve found it they will feed on the body in there.

And in fact they will then try to actually exit the suitcase as well,

and they can do this often through the holes in the frame

where the wheels of the suitcase are found.

So there's a whole range of factors out there in the environment

and even in the human factors of the environment

that can complicate the situation

and make it a real challenge for a forensic entomologist

to engage in any investigation.