Accumulated Degree Hours/days (ADH/ADD)
Definition
A temperature-corrected measure of thermal energy available for insect development, calculated by summing the degrees above a species-specific base temperature over time. ADH and ADD translate observed larval stage into elapsed time regardless of whether the weather was warm or cold.
- What it measures
- Thermal energy available for insect larval development, corrected for temperature
- Key application
- Converts observed larval stage into elapsed time for post-mortem interval estimation
- How it works
- Sum of (actual temperature minus species-specific base temperature) multiplied by time
Common questions
Why can't forensic entomologists just count calendar days to estimate how long a body has been there?+
Because insect larvae grow at different rates depending on temperature. A larva developing over 10 days in warm weather may reach the same stage as one that took 20 days in cold weather. To get an accurate elapsed time, entomologists convert raw calendar time into heat units using ADH/ADD, which normalizes for temperature variations.
How is ADH actually calculated?+
ADH is calculated by summing the degrees of temperature above a species-specific threshold, multiplied by time. For example, if a blow fly larva has a base temperature of 10°C, and the environment is 20°C for one day, that contributes 10 degree-hours. By matching the accumulated heat units to species-specific development tables, an entomologist can determine how much time has elapsed.
What's the practical benefit of using ADH/ADD for a death investigation?+
ADH/ADD makes post-mortem interval estimates more reliable across different climates and seasons. A body in cold winter weather or cool shade will show the same larval development stage as one in summer heat, but the actual elapsed time differs. Using temperature-corrected heat units lets investigators account for these differences and narrow down the timeline.
Related terms
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Explained in these topics
- Decomposition Stages and the Cadaver as a HabitatA temperature-corrected measure of thermal energy available for insect development, calculated by summing the degrees above a species-specific base temperature...
- Introduction and Scope of Forensic EntomologyA temperature-corrected measure of insect development time. Because larvae grow faster in heat and slower in cold, raw calendar time is converted into heat uni...