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.