During pupation, the larva contracts within its own integument so that the integument becomes a cylindrical puparium about 6.3 mm long.
Pupal stage of the house fly. A) Puparium ("pupal case") showing remains of the posterior and anterior spiracles of the larval stage. B) Pupa which develops inside the puparium. C) Puparium after adult fly has emerged through the anterior split
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The puparium gradually darkens to a rich, dark brown colour. Since the pupal case is formed by the larval skin, the pupa within is said to be coarctate.
The pseudocephalon is completely withdrawn, resulting in the anterior spiracular processes being very near the anterior end of the puparium.
Locomotor pads persist on the ventral surface although the puparium is immobile.
An obscure pair of pupal spiracles are in the conjunctiva between the fifth and sixth visible segments on the dorsal side; these are the only source of air for the pupa.
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