Body temperature, rigor and lividity are useful for estimating time of death only in the first day or two. After that, another clock takes over — one made of insects. Forensic entomology uses the creatures that colonise a body to estimate how long a person has been dead when other methods have run out.
A predictable succession
A body is colonised by insects in a fairly predictable order. Blowflies typically arrive first, often within minutes to hours, drawn by odour, and lay eggs in natural openings and wounds. Those eggs hatch into larvae (maggots) that feed and grow through defined stages before pupating and emerging as adults. Later, other insects and beetles arrive as decomposition advances. This succession is itself a rough timeline.
Reading the clock
The key is that insect development is temperature-dependent and species-specific. By:
- identifying the species present,
- measuring the developmental stage of the oldest larvae, and
- combining this with local temperature data,
an entomologist can estimate the minimum time since colonisation — which closely tracks the minimum time since death — across a window of days to weeks.
More than just timing
Insects can reveal other things too:
- Movement of a body — species that don't belong to where the body was found suggest it was moved.
- Toxicology — larvae that fed on the body can retain drugs or poisons (entomotoxicology), useful when conventional samples are gone.
The limits
It is still an estimate. Weather, season, whether the body was buried, wrapped or indoors, and delayed insect access all affect the result, so entomologists give a range and state their assumptions.
The bottom line
When the early post-mortem clues have faded, the life cycles playing out on a body become the most reliable clock available — a striking example of biology doing forensic work.