Forensic entomology | The crime scene
Summary
TLDRThis 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
🐛 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.
🔍 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.
Mindmap
Keywords
💡Insects
💡Post-mortem interval
💡Entomologist
💡Blowflies
💡Life cycle
💡Larvae
💡Pupariam
💡Forensics
💡Decomposition
💡Dispersal
💡Egg-laying site
💡Metamorphosis
💡Suitcase
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.
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