What this timeline produces
This tool takes the accumulated degree hour requirement for each of four developmental milestones and converts them into a timeline at a constant temperature, in hours and days.
Seeing the stages together shows how development accelerates and then extends — the first three transitions happen quickly, and pupariation accounts for most of the elapsed time. These tools are teaching aids. They are not validated for casework, and the reference values that make any result meaningful must come from published species-specific literature.
Stage thresholds
Before you build a timeline
- Every ADH figure must come from published data for the identified species. The defaults are round illustrative numbers, not reference values for any real species.
- The threshold must come from the same source as the requirements.
- The timeline assumes a constant temperature throughout, which no real scene provides.
- Requirements are cumulative from oviposition, not the duration of each individual stage.
Each figure is the total accumulated heat from egg-laying to that milestone, so the time shown is elapsed time since oviposition rather than the length of that stage. The duration of the third instar is the difference between the third instar and pupariation figures, not the pupariation figure itself.
How this calculator works
Each requirement divided by the same temperature difference:
Available heat per hour = temperature − lower threshold
For each stage: hours = stage ADH ÷ available heat per hour
Days = hours ÷ 24Because every stage uses the same divisor, the timeline scales uniformly with temperature. Raising the temperature compresses the whole sequence proportionally; it does not change the order or the relative spacing.
Worked example: 22°C with a 10°C threshold
Using the default figures — 22°C, a 10°C threshold, giving 12 degrees of available heat per hour:
- Egg hatch, 180 ADH: 15.0 hours (0.63 days)
- Second instar, 500 ADH: 41.7 hours (1.74 days)
- Third instar, 1,000 ADH: 83.3 hours (3.47 days)
- Pupariation, 2,500 ADH: 208.3 hours (8.68 days)
Note the shape. Reaching third instar takes three and a half days; reaching pupariation takes nearly nine. The third instar alone accounts for more than five days — more than everything before it combined. That is why third instar larvae are the most commonly recovered stage and why length measurement within that stage matters so much for narrowing an estimate.
Common mistakes
- Using the default ADH figures as real values. They are illustrative round numbers.
- Reading a stage figure as that stage's duration. They are cumulative from oviposition.
- Assuming a constant temperature. Real timelines are built from accumulated hourly data.
- Ignoring maggot mass heat in the later stages. Third instar aggregations run hottest.
- Omitting the pre-appearance interval. The timeline starts at oviposition, not at death.
Frequently asked questions
What happens after pupariation?
The larva forms a puparium and undergoes metamorphosis, emerging as an adult fly after a further substantial period — often as long again as everything preceding it. Empty puparia at a scene indicate at least one complete generation has passed, which extends the minimum interval considerably and is a distinct piece of evidence from live larvae.
Why does the third instar last so long?
It includes both the active feeding phase and the post-feeding wandering phase, during which larvae leave the body to find a pupariation site. Those are behaviourally very different but are frequently grouped together in developmental data. Whether recovered larvae are feeding or post-feeding is itself informative.
Do all blowflies follow this sequence?
The egg, three larval instars, pupa and adult sequence is common to blowflies, but the timings differ substantially between species and the same species develops differently at different temperatures. Some flies are also larviparous — depositing live larvae rather than eggs — which removes the egg stage entirely.
How does this fit with other post-mortem interval methods?
Entomology takes over where temperature-based methods lose value, typically beyond a day or two, and remains informative over weeks. The two are used together where both apply: a temperature estimate and an entomological minimum interval that agree provide stronger support than either alone.
Is what I enter stored?
No. Values are processed entirely in your browser and never transmitted or retained.
Related tools
References
- GOV.UK — Forensic Science Regulator codes of practice for forensic entomology
- Met Office — historic temperature data for reconstructing development conditions
Sources are checked at publication and can change — how I choose and check references.