”кр Eng


< Leonid I. Frantsevich >

Leonid Frantsevich. 2016. A Houdini's trick in a fly: leg unfolding with the aid of transient hinges in an extricating Calliphora vicina (Diptera: Calliphoridae). Arthropod Structure and Development 45, 2-13.


Legs in a fly pupa are tightly folded in Z-configuration: the femur points forward. The fly emerges from the pupa with all legs stretched backwards. How does the fly turn long femora inside the tight puparium? Flies were captured during emergence at various moments of progress out of the puparium and at once fixed in ethanol, postfixed in Bouin's solution. Specimens were ranged by the grade of progressive extrication and maturation. Legs were excised, their configurations photographed. Legs are anchored to the VIII. abdominal segment of the puparium with the pupal sheath. Some podomers were arched or buckled yet in pharate adults. At the initial moment of extrication, new buckles appeared in femora, they split femora into 2e3 subpodomers. Instead of turning the whole femur, the fly dragged through the puparium a chain of short subpodomers linked together with transient hinges. Hinges emerged in unsclerotized areas of the tubular podomer, close to sclerotized areas (juvenile sclerites). During extrication, legs were stretched passively. This process lasted for 1-3 min, initial phase Ц few seconds. Residual distortions were left in hind legs of free juvenile adults. Mechanics of buckling and straightening is discussed from the viewpoint of strength of materials.

Stages of metamorphosis in Calliphora vicina

(A) postfeeding larva; (B) empty puparium with parted valves; (C) pharate pupa; (D) pharate imago; (E) early stage of extrication, the big ptilinium is prominent; (F) late stage of extrication; (G) juvenile adult, able to walk; (H) mature live adult, consuming a honey drop.

Metamorphosis lasts for 10 days, extrication outside of the soil Ц only 1-3 minutes. Details are not seen inside an opaque confinement. Therefore, we fixed insects at different moments of eclosion and ranked them by their advance out of puparium.

Legs in the pharate adult are compactly packed in the zigzag configuration. (A) The pupa with the adult inside, excised from the puparium. The head and wings removed, view at the right body side. Black and white arrow indicates bending of the hind tibia about the right angle. (B-E) Configurations of separate legs: front (B), middle (C), and hind (D, E). (B-D) rear view, (E) front view. Podomers are indicated in (C): cx Ц coxa, th Ц trochanter, fm Ц femur, tb Ц tibia, ts Ц tarsus. The black arrow in (B) indicates the juvenile basal hinge in the femur, in (D, E) Ц arching of the tibia, arrows with white shades in (D) indicate juvenile sclerites: the distal one in the femur, the proximal one in the tibia. Scale bar 1 mm.

Flies get out of their puparia with straigtened legs, for this purpose they must turn the femur about 90°.

Compare the size of the puparium of a blowfly with the adult legs of the same fly: the leg has only scarce space for such maneuvres.

The fly does not turn its femora, but fractures them in pieces. These subpodomeres are joined with bucklings which function like transient hinges: they may flex and extend.

Details of leg deformations in extricating flies. (A-C) legs of the specimen of early rank 3; (D-F) legs of one specimen of late rank 8. (A, D) left front legs, front view; (B, E) right middle legs, rear view; (D, F) left hind legs, front view. Abbreviations: bh Ц basal femoral hinge, cx Ц coxa, fm Ц femur, mh Ц medial femoral hinge, tb Ц tibia, th - trochanter. Sclerotized parts of long podomeres are indicated in (D): dfs Ц distal femoral sclerite, and in (C): pts Ц proximal tibial sclerite. Scale bar 1 mm.

Instead of impossible turning of the femur about a blunt angle, the fly splits the femur in 2-3 transient subpodomeres and pulls the chain of short subpodomeres through the tight space inside the puparium. Later on, this chain is straightened, as well as the initially curved hind tibia.

Change of the leg configuration versus the progress of extrication. (Top row) front legs, (middle row) middle legs, (bottom row) hind legs. Legs were excised in 16 specimens and arranged in the rank order. Ranks 0 to 9 from the pharate imago to the free one are indicated above. Rear view. Scale bar 5 mm.

Buckling and stretching are applied to the legs passively, from the side of the imaginal trunk moving ahead by peristaltic bouts.

Reparation of residual leg deformations occurs during 1-2 hours of expansion and hardening (tanning) of the cuticle of an adult fly.


Series of papers:

2. Leg deformations and straightening during the swift ecdysis in the tight confinement:

- Ecdysis in a dragonfly

- Eclosion in Holometabola

- Extrication in a blowfly



I. I. Schmalhausen Institute of Zoology, 2004-2018