Forensic entomology
- Method
The insects that colonise a body, and how far they have developed, show the minimum time it has been exposed: a minimum postmortem interval.
What it is
Forensic entomology studies the insects found on a body, above all flies and beetles. Some flies lay eggs on a body soon after death if they can reach it, and their larvae grow at a rate that depends on temperature. Estimating the age of the oldest larvae, with the species' development data and the temperatures at the scene, gives the minimum time since the insects arrived: a minimum postmortem interval (minPMI), not the time of death. Later, the sequence in which different species arrive and leave (succession) helps over longer periods. Insects can also suggest that a body was moved, and they can be used for toxicology when no other tissue is left. The general approach to time since death, and how entomology fits with the other methods, is on the time since death page.
Accuracy and limits
- The result is a minimum interval, never the exact time of death.
- Accuracy depends on correct species identification, correct age estimation and good temperature data.
- Developmental data should come from the nearest geographic population.
- Each report should state the limits of each criterion used.
- Unrepresentative sampling or poor preservation reduces accuracy.
What it is based on
- Insect development speeds up with heat and slows with cold, in a predictable way for each species.
- Each species has its own developmental data, which vary between geographic populations.
- Large larval masses produce their own heat, which can speed development.
How it is applied
- Photograph the insects in place and note where on the body and around it they are.
- Collect the largest and most developed larvae, plus eggs, pupae, empty pupal cases and adults, including from the soil beneath.
- Kill and preserve part of each sample according to the entomologist's instructions; keep part alive for rearing.
- Record the temperature at the scene, of the body and of the larval masses, and the conditions (sun, shade, indoors, wrapping).
- Send labelled samples under chain of custody to an entomologist, with scene data and weather records.
- Read the result as a minimum interval and combine it with the other methods and the investigation.
Next step: what to do and document
- At the scene or the autopsy, collect insects before they leave or the body is washed or refrigerated.
- Record where the insects were, the scene temperature and the time of collection.
- In the report, describe the result as a minimum interval and explain what could delay colonisation.
- Consult a forensic entomologist; do not estimate the larvae's age without development data for the species and the place.
- Keep the samples under chain of custody like any other evidence.
Common mistakes
- Presenting the minimum interval as the time of death.
- Collecting only a few small larvae and missing the oldest ones.
- Preserving all specimens dead, so none can be reared to identify the species.
- Using weather-station temperatures without considering the conditions at the scene.
Test yourself
Think of the answer, then tap the question to see it.
What does forensic entomology estimate?
A minimum postmortem interval: the minimum time insects have been on the body, which may be shorter than the time since death.
Why is temperature so important in entomology?
Because insect development depends on temperature; errors in reconstructing scene temperatures are a main source of error.
Which larvae should be collected as a priority?
The largest and most developed ones, because they reflect the earliest colonisation.
Why might colonisation be delayed after death?
Because insects cannot reach the body: indoors, wrapped, buried, in cold weather or at night.
Connections
Educational content on forensic and legal medicine; not legal advice and no substitute for the technical guides of Colombia's National Institute of Legal Medicine and Forensic Sciences. Laws change: each page links the official text and says when it was last checked. For a real case, follow the guide in force and ask the competent authority.
Sources: Post-Mortem Interval Estimation Based on Insect Evidence: Current Challenges (Insects (Matuszewski S), 2021); The Forensic Entomology Case Report—A Global Perspective (Insects (Kotzé Z et al.), 2021); A Summary of Concepts, Procedures and Techniques Used by Forensic Entomologists and Proxies (Insects (Bambaradeniya TB, Magni PA, Dadour IR), 2023); The Minnesota Protocol on the Investigation of Potentially Unlawful Death (2016) (Office of the United Nations High Commissioner for Human Rights, 2017).
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Representative model, for educational purposes only.