Blowfly Colonization Begins
Blowflies locate remains within minutes of death.
- 2–10 min: Detection Time (after death outdoors)
- Calliphoridae: Primary Species (blowflies arrive first)
- >1 mile: Detection Range (via scent plumes)
- Variable: Season Factor (flies inactive below 10°C)
Scent-driven arrival
Decomposition gases attract flies from great distances.
Flies can arrive within minutes of death in daylight.
Species first responders
Calliphoridae and Sarcophagidae dominate the earliest wave.
Environmental gatekeepers
Cold, rain, or darkness delay initial colonization.
Oviposition at Natural Openings
Females deposit eggs in moist orifices and wounds.
- 150–250: Egg Cluster Size (eggs per batch)
- Eyes, nose, mouth: Preferred Sites (moist tissue first)
- 8–24 hrs: Egg Incubation (faster when warm)
- 3–8 wks: Female Lifespan (multiple batches laid)
Site selection
Moisture and odor guide precise egg placement.
Egg masses look like sawdust clumped near facial openings.
Batch oviposition
Hundreds of eggs cluster in a single mass.
Temperature dependence
Warmer conditions shorten time to hatching.
Larval Instars & the Feeding Mass
Larvae molt through three instars while feeding.
- 3: Instar Count (distinct growth stages)
- +10–20°C: Maggot Mass Heat (above ambient air)
- Degree Hours: Growth Driver (not clock time alone)
- 3–10 days: Feeding Duration (temperature dependent)
Instar progression
Each molt marks a measurable size increase.
Thermogenic mass
Dense larval clusters generate significant metabolic heat.
Maggot mass core temperature can exceed ambient by 20°C.
Degree-hour math
Entomologists convert growth into accumulated degree hours.
Post-Feeding Migration & Pupation
Mature larvae wander away before forming pupae.
- up to 30 ft: Migration Distance (from the body)
- Amber → brown: Puparium Color (hardens over time)
- 6–14 days: Pupal Duration (depends on species)
- 2–10 cm: Burial Depth (soil or debris)
Wandering phase
Larvae stop feeding and disperse from remains.
Puparium formation
The larval skin hardens into a protective case.
Forensic value
Pupal casings persist long after larvae disappear.
Empty puparia found nearby extend the estimated PMI window.
Insect Succession & Long-Term PMI
Later arrivals signal weeks to months since death.
- 4–8: Succession Waves (distinct species groups)
- Day 3+: Beetle Arrival (as tissue dries)
- Weeks–months: Late-Stage PMI (from beetle evidence)
- >20: Species Used (in casework globally)
Predictable waves
Each decomposition stage attracts characteristic insect species.
Beetles take over
Dermestid and rove beetles dominate drier remains.
Cross-referencing evidence
Multiple species present narrow the PMI estimate.
Combining maggot age with beetle succession refines PMI accuracy.