Spiracle
Definition
An external respiratory opening on the insect body wall. The morphology of the posterior spiracles is a primary character for identifying fly larvae to species and for confirming the instar.
- Location
- Posterior end of larval body (posterior spiracles)
- Function
- Gas exchange opening on the insect body wall
- Forensic use
- Species and instar identification in fly larvae
- Arrangement
- Typically paired, one plate per side
Common questions
Why do forensic entomologists focus on posterior spiracles rather than anterior ones?+
Posterior spiracle plates carry slit patterns and peritreme shapes that differ consistently between blow fly species and change predictably across larval instars, making them a reliable identification character. Anterior spiracles are smaller and less diagnostic.
Can spiracle morphology be examined without killing the larva?+
No, standard practice fixes the larva first, usually in hot water then ethanol or Kahle's solution, before mounting the posterior end for microscopy, since live larvae move and the cuticle can distort.
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- Instar
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