The Science of Decomposition: Unraveling the Mysteries of Insect Activity

• Human Regulation and Reproduction
• Further Education (Key Stage 5)

The Science of Decomposition: Unraveling the Mysteries of Insect Activity

27/02/2024

Learning Objective

At the end of the lesson, you will be able to understand the stages of decomposition, species change, and the impact of environmental factors on insect activity.

What do you already know about insect activity on the stages of decomposition?

Stages of Decomposition:

1. Fresh, Advanced, Active, Dry, Bloat
2. Bloat, Advanced, Active, Fresh, Dry
3. Fresh, Bloat, Active, Advanced, Dry
4. Fresh, Active, Bloat, Advanced, Dry

Insects and Arthropods

Are the primary organisms involved in decomposition of the

body

Arrive shortly after death – often less than 10 minutes

Insects and arthropods drawn to the decomposing body will be

unique to the area

What is Insect Succession?

Different groups of organisms find the 

body attractive at different stages of 

decomposition and the resultant 

change in the community is called 

succession. 

Colonisers 

1. Bacteria

2. Flies

3. Beetles (Rove, carrion, burrowing)

4. Parasitoid wasps

5. Cheese and coffin flies

6. Hide, ham and carcass beetles

7. Moth larvae and mites

* What conditions do they prefer? 
* How long do they tend to hang around? 

Necrophagous Species

• True flies - Diptera
• Blow flies - Calliphoridae
• Flesh flies - Sarcophagidae
• Beetles - Silphidae (Carrion) &
  Dermetidae (skin)

Usually arrive 1-14 days after death

Omnivorous Species

• Wasps and some beetles
• Feed on both the body and arthropods

Adventive Species

- Adventurous! Came from elsewhere

• Springtails, spiders, centipedes, millipedes
• Use the body as an extension of their own normal habitat

Accidentals

• Species that have no relationship to the body but are found there. 
• They may have fallen from surrounding vegetation or landed on the body because it has stopped flying

Factors: Temperature

Insects are cold blooded and sensitive to the environment

• Warmer climates accelerate insect development
• Cooler climates slow down / stop development of insects

e.g. Lucilia sericata (blow fly) requires surface temperature of 30oC before laying eggs.

Factors: Location

• Outdoor crime scene, more insects and more species
• Indoor crime scene, potentially less insects and less species

If the body is moved, may find insect from primary crime scene that are not native to the secondary crime scene.

What do cocaine and methamphetamine do to larvae development?

Speed up

Slow down

No idea

Morphine and Heroin do what to insect development?

Speed up

Slow down

No idea

Ethanol and alcohol do what to larvae development?

Speed up

Slow down

No idea

Insect Succession and Drugs/Alcohol

• Cocaine and methamphetamine - Accelerate development of larvae
• Morphine and heroin -  slow down development
• Ethanol and alcohol - Slow down the development

Insects and their faeces can be recovered and

tested for toxicology. 

Insect Succession and Burial / Covering 

• If you cover the body, it takes the insects longer to reach the remains, if at all. 
• Even a thin scattering of soil will prevent blow flies and flesh flies
• Some Diptera (fly) larvae can burrow to 10cm, and some beetles can inhabit deeper buried bodies, such as skin beetles. 

https://www.semanticscholar.org/paper/The-Affects-of-Clothing-on-Human-Decomposition%3A-for-Miller/f343ea0581e40d4f58f0e935cfe10b239592c43c

Insect Succession and Submersion 

• In Seawater, flesh is eaten by crabs, shrimp, other crustaceans and fish
• In fresh water, water beetles and caddisfly larvae feed on the deceased
• Otherwise, the presence of insects indicates that the death occurred on land
• (If frozen, insects will only colonise if the body is placed outside.)

How do we collect the insects? 

• Trap and collect flies with nets 
• 50-60 larvae should be collected from the maggot mass
• Living larvae should be collected and shipped to the forensic entomologist for rearing purposes - With a food source, such as beef or chicken liver. 

The Killing Jar

• Glass container with cotton balls or plaster soaked in ethyl acetate, ether, or chloroform. 
• Jar is capped and flies immobilised within minutes
• Flies then transferred to jar of 70% ethyl alcohol for preservation. 

Forensic Entomology Data Form

What information is included? 

• General habitat and location of body in reference to
  vegetation, sun, shade, etc. 
• Locations of insect infestations on the body
• Stages of insects observed
• Evidence of scavenging from animals and predation of
  eggs and larvae by other insects. 

Other Special Considerations

• All techniques should be thoroughly documented 
• If the body has more than one site of colonisation, each site should be treated separately
• Get a good representation of various sized larvae present
• Jar label should be in graphite / pencil, not ink

What is the primary role of insects in forensic entomology?

1. Cleaning up crime scenes
2. Assisting in DNA analysis
3. Aiding in estimating the post-mortem interval
4. Providing evidence of the cause of death

Which stage of insect succession in forensic entomology occurs first?

1. Post-decay
2. Fresh
3. Dry remains
4. Decomposition

What is the study of insects and their relationship to a crime scene called?

1. Crime scene entomology
2. Criminal entomology
3. Forensic entomology
4. Insectology

What is the term for the process of insects colonizing a body after death?

1. Insect succession
2. Carcass infestation
3. Post-mortem colonisation
4. Maggot migration

Which insect is commonly used to estimate the post-mortem interval in forensic entomology?

1. Butterfly
2. Ant
3. Blow fly
4. Ladybird

Write down 3 things you learned in this lesson.

Have students enter three things they learned in this lesson. With this they can indicate their own learning efficiency of this lesson.

Write down 2 things you want to know more about.

Here, students enter two things they would like to know more about. This not only increases involvement, but also gives them more ownership.

Ask 1 question about something you haven't quite understood yet.

The students indicate here (in question form) with which part of the material they still have difficulty. For the teacher, this not only provides insight into the extent to which the students understand/master the material, but also a good starting point for the next lesson.