Instar
Definition
A developmental stage between moults (ecdysis). Blow flies have three larval instars (L1, L2, L3), each ending when the larva sheds its cuticle. Instar identity is the first thing a forensic entomologist determines when examining a larval specimen.
- Blow fly larval instars
- Three instars (L1, L2, L3) before pupation
- First instar
- Smallest stage, recently hatched
- Third instar
- Largest stage, enters the wandering phase to pupate
- Identification markers
- Size, mouthpart morphology, and spiracle structure
Common questions
What exactly is an instar?+
An instar is a larval stage that occurs between two moults (when the larva sheds its outer skin). Blow fly larvae go through three instars, each one larger than the last, and forensic entomologists identify which instar they are examining by looking at the size, mouthpart shape, and spiracle structure of the specimen.
How do forensic entomologists use instar information?+
Determining instar is the first thing a forensic entomologist does when examining a larval specimen because it helps estimate the age of the insect and therefore the time since death. The third instar is the largest and enters the wandering stage, when the larva leaves the body to find soil and pupate.
Why do blow flies have multiple instars?+
Each instar represents a growth phase. Blow fly larvae must shed their rigid outer skin to get bigger. After three larval instars, the larva transitions to the pupal stage, where it undergoes metamorphosis into an adult fly.
Related terms
- Accumulated Degree Hours (ADH)
- A temperature-corrected measure of developmental time. Calculated by summing (hourly ambient temperature minus the species-specific base temperature threshold) across the period of...
- Base Temperature
- The species-specific temperature below which development effectively ceases. For most forensically relevant blow fly species this is in the range of 2-10...
- Binomial Nomenclature
- The two-part Latin naming system established by Linnaeus: genus name followed by species epithet. Used in all scientific and forensic botanical reports...
- Body Bag
- The sealed bag used to transport the body from scene to mortuary. Treated as a collection zone because migrating larvae, puparia, and...
- Calliphoridae
- The blowfly family: metallic-coloured flies that are typically the earliest colonisers of exposed remains. Forensically important genera include Calliphora, Lucilia, Chrysomya, and...
- COI Barcoding
- DNA-based species identification using a standard 658 bp segment of the mitochondrial cytochrome oxidase subunit I gene. Sequences are matched against reference...
- External Examination
- The stage of the autopsy in which the pathologist examines the body surface, documents injuries, and removes clothing before any incisions are...
- Hemimetabolous
- A developmental pattern with three stages (egg, nymph, adult) and no pupal stage. Nymphs resemble small adults and moult repeatedly. Cockroaches and...
- Holometabolous
- A developmental pattern with four distinct stages (egg, larva, pupa, adult) and a complete metamorphosis inside the pupal case. Flies, beetles, and...
- Internal Cavity Insects
- Larvae or puparia found inside the skull, thorax, or abdomen during internal autopsy examination. They often represent colonisation through wounds or extended...
- Maggot Mass Documentation
- The photographic and physical record of each maggot mass location, volume, instar, and temperature taken at the start of autopsy before any...
- Post-Mortem Interval (PMI)
- The time elapsed between death and discovery or examination of remains. PMI estimation draws on multiple disciplines: soft tissue decomposition stage, insect...
Explained in these topics
- Collection at Autopsy and from the BodyA distinct larval stage between moults. Blow fly larvae pass through three instars before the pupal stage. First instar is the smallest, recently hatched; thir...
- Entomological Evidence and Post-Mortem Interval EstimationA larval stage between moults. Calliphorid larvae pass through three instars (L1, L2, L3) before forming a pupal case. The instar stage and larval length, comb...
- Insect Biology and Taxonomy for the Forensic EntomologistA larval stage between two moults. Blow fly larvae pass through three instars. The stage is identified by size, mouthpart morphology, and spiracle structure.
- The Blow Fly Life Cycle: Egg to AdultA developmental stage between moults (ecdysis). Blow flies have three larval instars (L1, L2, L3), each ending when the larva sheds its cuticle. Instar identit...