Укр Eng


< Leonid I. Frantsevich >

Leonid Frantsevich, Iryna Kozeretska, Yuriy Dubrovsky, Tatyana Markina, Iryna Shumakova, and Stanislav Stukalyuk. 2017. Transient leg deformations during eclosion out of a eight confinement: a comparative study on seven species of flies, moths, ants and bees. Arthropod Structure and Development 46, 483-495..


Legs in dipteran pupae are tightly packed in a zigzag configuration. Changes in the shape or configuration of long podomeres during eclosion have been overlooked because they occur rapidly (in a few minutes) and the legs are hidden inside a tight opaque confinement: the puparium in the Cyclorrhapha, the obtect pupa in mosquitoes. We fixed insects at different times during eclosion and obtained a temporal description of changes in leg shape. At the start of eclosion in Calliphora vicina and Drosophila melanogaster, femora are buckled in between the joints. Later, the chain of podomeres straightened, pointing posterad. Initial deformation and further stretching were passive, exerted by forces external to the legs. The prerequisites for this are pliability of the tubular podomeres and anchoring of the tarsi to the confinement. Each femur was strongly crooked instead of buckled in the mosquito Aedes cantans. The site of bending shifted distad in the course of eclosion: a sort of peeling. In contrast, other insects (the moth Bombyx mori, the ants Formica polyctena and F. rufa, the honey bee Apis mellifera) left their tight confinements without any change in the initial zigzag leg configuration and without transient deformations of initially straight femora and tibiae.

Larvae in holometabolous insects are adapted for feeding and growth, legs in most of species are either short or absent at all. Metamorphosis into the adult insect occurs in a quiescent pupa, with immobile wing vestiges and tightly packed legs. Pupae are often protected by silk cocoons, artificial nest cells, or puparia (hardened larval integuments)

Pupa of a house fly, Musca domestica. (A) Drawing from Hewitt (1914); (B) original SEM photograph (specimen by L. F., SEM by J. Berger). Legs of the pupa are packed in the zigzag configuration. The arrow indicates direction of the hidden femur.

Z-configuration of legs in pupae. Legs are arranged in the order: R1 (front), R2 (middle), R3 (hind), as indicated in (F). (A) Calliphora vicina, (B) Drosophila melanogaster, (C) Aedes cantans, head and wing vestige ablated, tarsi recurved, (D) Bombyx mori, (E) Apis melliphera, (F) Formica rufa. Femora and tibiae are often bent in (A-C), but straight in (D-F), tarsi recurved in (C).

However, flies emerge from their pupa with straighten legs: eclosion of a mosquitoe from the film “Microcosmos”.

(click the image to watch the video in a separate window)

There is no empty place inside the tight confinement in order to turn the femur about 180°.

Confinements protecting the pupa: (A) puparium in Calliphora vicina, one valve of the operculum is shed; (B) puparium in Drosophila melanogaster, with the pharate imago inside; (C) cocoon of Formica polyctena, with the pupa inside; (D) hard swimming pupa of Aedes cantans; (E) hexahedral wax cell of Apis mellifera, sealed, one facet removed: the silk cocoon covers the cell, a small part of the cocoon over the exposed head is removed; (F) same, the cocoon removed, the pupa is exposed; (G) dense silk cocoon of Bombyx mori after emergence of the moth through the orifice at the left.

(Top row) Calliphora vicina, (middle row) Drosophila melanogaster, (bottom row) Aedes cantans. Leg configurations in ranked specimens demonstrate initial leg deformations and further straightening.

Leg configurations in eclosing imagines of Aedes cantans. (Top row) front legs, (middle row) middle legs, (bottom row) hind legs. Ranks are indicated in the middle row.

Representative leg configurations in Drosophila melanogaster, arranged by the grade of leg stretching. (Top row) front legs, (middle row) middle legs, (bottom row) hind legs. Ranks by the advance of the body are indicated at the tarsi of specimens. Buckling of the hind femur occurs later than in the front and middle legs. Legs of ten specimens of different size are depicted. Scale bar 1 mm.

Leg ranking for Calliphora vicina is illustrated in the separate article.

Deformations of the femur affect early ranks and are of different type in mosquitoes and cyclorrhaphan flies.

(A) Buckling of the femur in Calliphora vicina; (B) buckling in Drosophila melanogaster, (C) crooking in Aedes cantans.

Position of crooking in the mosquito shifts distally part during eclosion and thus resembles peeling.

In difference to flies, no leg deformation in the silk worm, Bombyx mori (Lepidoptera), in the honey bee, Apis mellifera, and in the ants Formica rufa nd F. polyctena (Hymenoptera) occurs during their eclosion.

Partial leg stretching without podomere deformation during eclosion in Bombyx mori. Top row – moths eclosing from free pupae. Lower three rows – legs in the same specimens.

When the moth molts inside the cocoon, it sheds its pupal exuvia and only afterwards dissolves the silk and makes the opening in the cocoon: note the adult moth plus two exuviae – the big one is the integument, the small one is the caterpillar’s integument shed after weaving of the cocoon.

Presumably, bees and ants also left their pupal integuments before extrication from their cocoons or wax cells. We traced leg configurations in insects still hidden inside their confinements.

Pupal integument in honeybees and two ant species is soft. No traces of leg deformation or stretching of the Z- configuration was noticed in bees. The molted bee gnaws its way out of the wax cell.

Zigzag leg configurations in workers of Formica polyctena, released from cocoons by adult workers.

Why for eclosion behavior and leg biomechanics are different in Holometabola from other Arthropoda? The pupa in holometabolans lacks any substrate for leg grasping. Presumably, the pupal leg sheath is thin and soft at its inner side and is torn by adult legs if the legs are hard. Or, if adult legs are pliant, they demonstrate other types of deformation comparing to squeezing in the rest of arthropods.


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