Detailed entomological calculations
Step 1. Determine temperature history at crime scene
- Extract weather bureau records of maximum and minimum daily temperatures at the weather station nearest to crime scene, over the general period the body has been exposed.
- Set up weather station at crime scene (after body has been found) and compare temperature changes with those at the nearest weather station. Calibrate the weather bureau data for the period preceding discovery of the body, accounting for differences between crime scene and weather station.
- Calculate the average temperature that the body has been exposed to.
Step 2. Rear maggots to adulthood to identify species
- Collect a range of maggots, (particularly those that might be the oldest) from the body and rear them (on ox-liver) at constant temperature.
- Record time taken until larvae pupate.
- Keep pupae until adults emerge.
- Identify fly species from adult characteristics. (For some species, identification from larval features may be possible or they can be identified from DNA samples, if a DNA library is available.)
Step 3. Estimate time of egg laying
- Using knowledge of development rate of the particular species at rearing temperature, count back to estimate age of maggots when body found.
- Using knowledge of development rate* of the particular species at the average crime scene temperature, count back to determine date of egg laying.
- This is the latest time at which the body died. (It may have died earlier if there was a delay between death and egg laying. This depends on weather conditions and accessibility of the body to insects).
* If the development rate of the particular species at a range of temperatures is unknown (which is the case for most Australian flies), the emergent flies can be used as breeding stock. Eggs can be reared at temperature conditions corresponding to those estimated for the crime scene, to determine development rate.
Step 4. What other insect evidence is available?
- Do steps 1-3 for all the different insect types found at the crime scene to improve accuracy of determination.
Further information
- Criminal case history
- Fly life cycle
- Development times of Lucilia sericata at different temperatures
Copyright © Australian Museum 2003
