Insects and plants provide crucial evidence for estimating time since death and connecting suspects to crime scenes.
Forensic entomology is the study of insects and other arthropods in the context of legal investigations. Its primary application is estimating the post-mortem interval (PMI) — the time elapsed since death — by analysing insect evidence found on or near human remains.
The science is grounded in a simple principle: insects colonise a body in predictable, well-documented patterns. Different species arrive at different stages of decomposition, and their larvae develop at rates determined by temperature and species. By identifying the species present and measuring the developmental stage of the oldest specimens, entomologists can calculate a minimum PMI with remarkable accuracy.
Blowfly Colonisation Timeline
Death Occurs
Blowflies Arrive
minutes – hours
Eggs Laid
natural openings & wounds
Larvae Develop
1st → 2nd → 3rd instar
Pupation
pupal casing forms
Adult Emergence
As a body decomposes, it passes through distinct stages — fresh, bloat, active decay, advanced decay, and dry remains. Each stage attracts a characteristic community of insects, arriving in predictable waves. This sequential pattern of colonisation is called insect succession, and it provides forensic entomologists with a biological clock for estimating how long a body has been exposed.
minutes – hours
The first insects to arrive, often within minutes of death. Female blowflies are attracted by the gases released during early decomposition and lay hundreds of eggs in natural openings (eyes, nose, mouth) and any wounds. Their larvae — maggots — are the primary tool for estimating short-term PMI.
days
Flesh flies (Sarcophagidae) arrive as the body enters the bloat stage. Unlike blowflies, many flesh fly species deposit live larvae rather than eggs. Rove beetles and hister beetles also appear, feeding on both the remains and the maggots from Wave 1.
weeks
During advanced decay, dermestid beetles (Dermestidae) colonise the remains, feeding on dried skin and cartilage. Cheese skippers (Piophilidae) — named for their larvae's ability to jump — are also characteristic of this stage. Their presence indicates the body has been exposed for several weeks.
months
In the final dry-remains stage, clothes moths (Tineidae) and various mite species feed on hair, dried tissue, and any remaining organic material. Their presence indicates a PMI of months or longer, and they are often the last arthropods associated with remains.
Quick Check
Which insects are typically the first to colonize a body after death?
Forensic entomologists use two complementary methods to estimate the post-mortem interval, each suited to different timeframes.
The most precise method for short-term PMI (hours to weeks). Entomologists identify the species and developmental stage (instar) of the oldest larvae on the body.
Because larval development is temperature-dependent, scientists use Accumulated Degree Hours (ADH) or Accumulated Degree Days (ADD) — the cumulative heat units above a species-specific minimum developmental temperature — to back-calculate when eggs were first laid.
More useful for longer PMIs (weeks to months). Instead of measuring individual larval development, this method examines which waves of insects are present or absent on the remains.
Each decomposition stage attracts a characteristic insect community. By comparing the species assemblage found on the body to known succession patterns for the local environment and climate, entomologists can estimate the period of insect activity — and therefore the minimum PMI.
Fill in the Blank
The minimum time since death, estimated by studying insect evidence, is called the minimum________.
Forensic botany is the application of plant science to legal investigations. Plant evidence — from microscopic pollen grains to entire root systems — can link suspects to crime scenes, establish timelines, and determine whether a drowning victim was alive when they entered the water.
Pollen Analysis (Palynology)
Microscopic pollen grains can link a suspect to a specific geographic location. Pollen is nearly indestructible, highly resistant to decay, and its composition varies with location and season — making it a powerful trace evidence tool.
Diatom Analysis
Diatoms are microscopic silica-shelled algae found in virtually all water. In drowning cases, if diatoms are found in organs such as bone marrow, it confirms the person was alive when they entered the water — a critical distinction in death investigation.
Plant DNA
DNA extracted from plant material found on clothing, vehicles, or tools can identify the specific species and even the individual plant at a crime scene, connecting a suspect to a precise location.
Growth Patterns
Tree rings (dendrochronology), moss growth, root penetration, and plant growth over buried objects can all indicate elapsed time — helping investigators establish when a body was buried or an area was disturbed.
“A handful of soil from a crime scene can contain thousands of pollen grains, each one a potential witness that can place a suspect at the scene with remarkable geographic precision.”
— Patricia Wiltshire, Forensic Ecologist
Quick Check
Why are diatoms useful in drowning investigations?
Fill in the Blank
The study of pollen grains, which can link a suspect to a specific geographic location, is called________.
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