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Forensic Entomology · Tools
Estimate minimum post-mortem interval from accumulated degree hours for an insect development stage.
ADH = (T − T_base) × hours
Accumulated degree hours and days
Species specific. Around 10 °C for Calliphoridae, 11 °C for Chrysomya, 8 °C for Lucilia.
From a development table for the identified species and stage.
Estimated time to reach the stage
10.42days
ADH = (T - T_base) x hours => hours = 4000 / (26 - 10) = 250.0 h
This is the minimum post-mortem interval: it dates colonisation, which cannot be earlier than death but may be later. Use retrospective weather data corrected to the scene, not a single mean.
Accumulated degree days require a correctly identified species, a validated development dataset for that species, and scene-corrected temperature data from the nearest weather station. Development is non-linear near both thermal limits, and maggot-mass heat can raise local temperature well above ambient. The result is a minimum PMI only.
Insects are poikilothermic, so their development depends on accumulated heat rather than elapsed time. Above a species-specific lower threshold, development accrues in proportion to how far the temperature exceeds that threshold, measured in degree hours or degree days.
Working backwards from the stage found on a body, with a validated development dataset for the identified species, gives the time needed to reach it. That dates colonisation, which is a minimum post-mortem interval.