Skip to content

Quiz: Forensic Entomology and Decomposition Analysis

Test your understanding of decomposition stages, blowfly lifecycle, ADH calculations, insect succession ecology, and environmental variables with these questions.

1. Which insect family is typically the first to colonize remains after death under most outdoor conditions, and why are they forensically important?

  1. Dermestidae (hide beetles) — because they arrive immediately and consume all soft tissue
  2. Sarcophagidae (flesh flies) — because they give birth to live larvae, which begin development before blowfly eggs hatch
  3. Calliphoridae (blowflies) — because they are first colonizers whose highly predictable, temperature-dependent development provides the primary basis for minimum PMI estimation
  4. Silphidae (carrion beetles) — because their wing covers preserve specimens well enough for species identification
Show Answer

The correct answer is C. Calliphoridae (blowflies) are typically the first insect colonizers of remains under most conditions. Adult females detect volatile compounds released during the earliest stages of autolysis and putrefaction from distances of kilometers, arriving within minutes to hours of death in warm conditions. Their development times relative to temperature are extensively studied and published. The age of the oldest blowfly specimen found on remains establishes the minimum post-mortem interval (mPMI) — the earliest possible time of death.

Concept Tested: Calliphoridae Family

2. During which decomposition stage does visible abdominal swelling occur, and what causes it?

  1. Fresh stage — as autolysis destroys cell membranes, fluid shifts from cells into the abdominal cavity
  2. Bloat stage — putrefactive bacteria produce gases (hydrogen sulfide, methane, ammonia) that create pressure distending the abdominal cavity
  3. Active decay stage — maggot mass metabolic activity generates heat that expands trapped gases within the body
  4. Advanced decay stage — desiccation causes the remaining tissues to contract, creating the appearance of swelling relative to bone structure
Show Answer

The correct answer is B. The bloat stage is characterized by visible abdominal swelling caused by putrefactive bacteria producing gases — primarily hydrogen sulfide, methane, ammonia, and carbon dioxide — as they decompose internal organs. These gases create internal pressure that distends the abdomen visibly, forces purge fluid from body openings, and generates the intense odors that attract additional insect species and scavengers. The bloat stage typically begins within 1–4 days in warm weather but may not occur at all in very cold conditions.

Concept Tested: Bloat Stage of Decomposition

3. A forensic entomologist collects third instar blowfly larvae from remains. The published ADH requirement for third instar completion in the identified species (base temperature 2°C) is 258 ADH. The ambient temperature has been a constant 22°C for the past 24 hours. How many accumulated degree hours does this represent, and is it sufficient to explain the observed development?

  1. 22 ADH — insufficient; the development would require 11.7 days at this temperature to reach third instar
  2. 480 ADH — far exceeding the 258 ADH threshold; more than enough for third instar development in 24 hours
  3. 240 ADH — just below the threshold; the larva is almost to third instar but not quite there
  4. 528 ADH — only half the required threshold because the formula divides by 2 for the instar number
Show Answer

The correct answer is B. Accumulated Degree Hours for 24 hours at 22°C with a base temperature of 2°C: ADH = (22 − 2) × 24 = 20 × 24 = 480 ADH. This exceeds the 258 ADH threshold for third instar completion, meaning 24 hours at 22°C is more than sufficient to explain full third instar development. The mPMI would be calculated by working backward through the temperature record to find when the cumulative ADH first equaled 258, which in this case would be partway through the previous day. Third instar would have been reached before the end of 24 hours.

Concept Tested: Accumulated Degree Hours

4. The minimum post-mortem interval (mPMI) represents the earliest possible death date based on insect evidence. Why is the actual time of death often earlier than the mPMI?

  1. Laboratory analysis of insects takes several days, during which additional development occurs that is not accounted for in the calculation
  2. Blowflies may not have had immediate access to the remains, or bad weather may have suppressed oviposition, meaning death could have preceded the first oviposition by hours or days
  3. The ADH formula systematically underestimates development time, introducing a conservative bias of several days
  4. The mPMI calculation assumes a base temperature of 0°C, but actual base temperatures are always higher, making the estimate too early
Show Answer

The correct answer is B. The mPMI is based on when blowfly oviposition (egg laying) began, not necessarily when death occurred. Death may have preceded the first oviposition for several reasons: the body may have been indoors or covered, preventing immediate fly access; cold weather, rain, or nighttime conditions may have suppressed oviposition; or the body may have been moved after death. Any of these circumstances would create a gap between the time of death and the first colonization event. The mPMI represents the minimum time elapsed — actual death could have been earlier.

Concept Tested: Minimum Post-Mortem Interval

5. During the active decay stage, a maggot mass can raise its own local temperature 10–15°C above ambient. What effect does this maggot-mass-generated heat have on development rates?

  1. It slows development because the elevated temperature denatures the enzymes the larvae use for digestion
  2. It accelerates larval development because ADH accumulates faster at higher temperatures, completing the developmental stages more rapidly than ambient temperature alone would predict
  3. It has no effect on development rates because larval enzymes are calibrated to ambient temperature, not maggot mass temperature
  4. It causes developmental arrest because the elevated temperature triggers a heat-stress response in the larvae
Show Answer

The correct answer is B. Maggot mass metabolic heat raises the local temperature around the larvae significantly above ambient. Because insect development rate is directly proportional to temperature above the base temperature (as expressed in the ADH formula), this self-generated heat accelerates the larvae's own development. A maggot mass at 35°C in a 22°C environment accumulates degree hours at a much faster rate than ambient temperature calculations would predict. This is why entomologists using ADH calculations must account for maggot mass temperature when available — ambient temperature records alone can underestimate development speed.

Concept Tested: Larval Instar Stages

6. During insect succession, which insect family tends to dominate the advanced and dry remains stages, after blowfly activity has subsided?

  1. Calliphoridae (blowflies) continue to dominate throughout all stages because of their reproductive advantage
  2. Dermestidae (hide beetles) and other secondary consumers that feed on dry tissue, keratin, and fat as tissue becomes desiccated
  3. Sarcophagidae (flesh flies) replace blowflies in the advanced decay stage because they prefer dry tissue
  4. Hymenoptera (wasps and ants) dominate the dry remains stage because they extract bone marrow
Show Answer

The correct answer is B. Insect succession at remains follows a predictable ecological pattern as the substrate changes. Blowflies dominate early stages when soft, moist tissue is available. As tissue dries and the most accessible food is consumed, secondary consumers arrive — including dermestid beetles (Dermestidae, or hide beetles) that feed on dry tissue, fat, and keratin (hair, nails, dried skin). Moth larvae (Tineidae) may feed on hair and dry tissue. This sequential wave pattern means the presence of dermestid beetles and absence of active blowfly larvae indicates the remains are in a later decomposition stage.

Concept Tested: Insect Succession Ecology

7. A body is found indoors in a sealed apartment during summer. The investigator notes the absence of blowfly eggs or larvae, even though the body shows significant decomposition. What environmental variable most likely explains the absence of insect activity?

  1. Indoor temperature — sealed apartments are too cold in summer for blowfly development
  2. Restricted insect access — blowflies could not enter the sealed indoor environment, preventing colonization despite favorable decomposition conditions
  3. Absence of moisture — indoor environments are too dry for blowfly oviposition, even in summer
  4. Chemical contamination — indoor paint and synthetic materials produce compounds toxic to blowflies at any concentration
Show Answer

The correct answer is B. Insect access to remains is a critical environmental variable. In sealed indoor environments, blowflies may be completely excluded even when outdoor conditions would allow immediate colonization. Without access, no oviposition occurs, and the entomological clock never starts. This is why the absence of insects does not mean death is recent — it may simply mean insects were excluded. Investigators must consider building sealing, windows, doors, and ventilation status when interpreting the absence of insect evidence in indoor cases.

Concept Tested: Environmental Variables in PMI

8. What is entomotoxicology, and what information can it provide that standard toxicology on decomposed remains cannot?

  1. The study of insect-transmitted disease; it identifies pathogens introduced to remains by insect activity
  2. The analysis of drugs and poisons in maggot tissue, which can reveal the drug levels in the victim at the time of death when soft tissue is no longer available for standard toxicology
  3. The examination of toxic compounds produced by insects during decomposition that can simulate poisoning in the toxicological profile
  4. A technique to detect insecticide residues on remains, indicating that someone attempted to accelerate or suppress decomposition
Show Answer

The correct answer is B. Entomotoxicology is the analysis of drug and poison concentrations in insect tissues — particularly maggot tissue. When soft tissue has decomposed beyond the point where standard toxicology can be performed, larvae feeding on those tissues may retain detectable concentrations of drugs or poisons from the victim's body. By analyzing maggot tissue, toxicologists can estimate what drugs were present in the victim at the time of death. Additionally, drugs and chemical contamination can alter insect development rates, which must be factored into mPMI calculations.

Concept Tested: Environmental Variables in PMI

9. Blowfly puparia are often found in the soil beneath a body. Why are these forensically valuable even when all larvae have already emerged as adults?

  1. Empty puparia indicate that the body was moved after decomposition, because puparia only form away from the remains
  2. Puparia from earlier colonization cycles may represent an older developmental stage than surface larvae, providing a longer minimum PMI estimate, and species can be confirmed by rearing any remaining pupae to adult emergence
  3. Puparia contain intact DNA from the larvae inside, allowing species identification without rearing to adulthood
  4. The presence of puparia proves the body was outdoors, because blowflies cannot pupate in indoor environments
Show Answer

The correct answer is B. Third instar larvae migrate from the remains to find a suitable dry pupation site — typically in soil near the body. Puparia from earlier colonization cycles may therefore be older than the current surface larvae, providing a longer minimum PMI window. Collecting both surface larvae and soil-collected puparia gives the most complete developmental picture. Some puparia may contain partially or fully developed adults that can be reared to confirm species identification. Species-level identification is critical because different species have different published ADH requirements, and using the wrong species' data would produce an inaccurate PMI.

Concept Tested: Blowfly Pupa Stage

10. Why is temperature considered the primary environmental variable governing insect development and decomposition rates?

  1. Temperature determines the moisture content of the body, which controls how quickly bacteria can multiply and begin putrefaction
  2. Temperature directly controls the rate of enzymatic and metabolic reactions in insects, with development proceeding proportionally to temperature above the base developmental threshold
  3. Temperature affects the availability of oxygen for both insect respiration and aerobic bacterial decomposition
  4. Temperature is the only variable that can be accurately measured at the scene, making it the only practical variable to include in PMI calculations
Show Answer

The correct answer is B. Temperature is the primary driver because insect development is governed by biochemical reactions — enzyme activity, cellular metabolism, and growth — all of which are temperature-dependent. Within the species' viable range, development proceeds at a rate proportional to the temperature above the base developmental temperature (expressed mathematically as ADH or ADD). Temperatures below the base temperature pause development; higher temperatures accelerate it. This direct, quantifiable relationship between temperature and development time is what makes the ADH/ADD model mathematically tractable for mPMI calculations.

Concept Tested: Accumulated Degree Days