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< Leonid I. Frantsevich >

Leonid Frantsevich, Zhendong Dai, Wei Ying Wang, Yafeng Zhang

Geometry of Elytra Opening and Closing in some Beetles (Coleoptera, Polyphaga).

Journal of Experimental Biology 2005, 208: 3145-3158.

Summary. Elytra in beetles move actively, driven by their own muscles, only during transient opening and closing. The kinematics of these movements has been inadequately described, sometimes controversially. Our goal was a quantitative 3D description of diverse active movements of the elytra, in terms of directions of the axes of elytra rotation.

Broad opening and closing was videorecorded in beetles, tethered by the mesothorax, and has been analyzed frame by frame. For tracing, small dots or straw arms have been glued to the elytra. Opening and closing traces coincided. The trace of the elytron apex was a flat circular arc about the axis of abduction-adduction (AAA). The rising hemiaxis pointed contralaterad. The AAA was tilted forwards in Melolontha hippocastani, Allomyrina dichotoma and Prionus coriarius but backward in Chalcophora mariana. In Cetonia aurata, AAA had low elevation and a strong backward orientation. If another elytra-fixed point was traced in addition to the apex (in M. hippocastani and P. coriarius), then secondary rotation about the sutural edge (supination on opening) occured.

Modeling of abduction-adduction revealed that the elytron rose on opening if the AAA pointed contralaterad. The more the AAA was tilted forward, the more negative was the attack angle of the open elytra. The negative attack angle was partly compensated by positive body pitch and, more effectively, by supination of the costal edge about the sutural edge. The initial stage of opening included elevation of closed elytra (by 10-12°) and partition to the sides, combined with an inward turn (< 2-3°). Axis of rotation at this stage presumably coincided with the AAA. Movement of one elytron with respect to the opposite one at the beginning of opening followed the shallow arc convex down. The geometry of this relative movement describes the initial partition of the elytra and release of the sutural lock.

Tethered flight of Melolontha hippocastani

The insect is filmed under a skew mirror: the top image is in the mirror, the bottom one is real. Frame coordinates of any corresponding points in two images are transformed into 3D coordinates in the global space. In the experiment, a videocamera is tilted about 90° to fit both images to the landscape format.

Dots on the wing are used for easy tracing

Traces of landmark dots on the elytra in a cockchafer Melolontha hippocastani
in two projections in the external reference system during opening (hollow dots)
and closing (black dots).

Tethered flight of a cerambycid Prionus coriarius

Light orthogonal tripods are glued to the elytra. They show complicated rotation of the elytron during opening and closing.



The apex of the elytron rotates down a flat circular arc, the same one during opening (hollow dots) and closing (black dots). The axis of rotation is skew with respect to the body. Parallel traces (box in the top panel) are simultaneous rising of both elytra at the start of opening and sinking down at the finish of closing. Traces of flight strokes of the elytra after opening and before closing are seen as mushroom heads: their axes of rotation are parallel to the longitudinal body axis. Moreover, during opening and closing the elytron rotates additionally about the costal edge, supinating or pronating.

Modeling of elytra motion. Left column - abduction of the left elytron by 90° versus different azimuth of the rotation axis (AAA). The less the azimuth, the more the open elytron tends to negative attack angle. Right column - supination combined with abduction. D - supination of two elytra without abduction. E, F - supinatory compensation of the attack angle to zero in the abducted left elytron. Initial position of elytra in A-E is horizontal, in F bent down. Angular variables are indicated in the panels: azimuth φ, elevation ψ, abduction α, bend β, supination σ. Isometric view in the body-fixed reference frame.

Profile of the frictional locking sutural structures in a dung beetle, Catharsius molossus is typical for most beetles. We must take into account that elytra move relative each other during unlocking or locking. The trajectory of relative motion is not a simple circle.

We model it for the imaginary 360° rotation of each elytron: A – closed and open positions of two elytra, B – intermediate stages of opening in the body-fixed coordinates, C –an observer sitting on the moving elytron views the opposite elytron, also moving, D – relative trajectory of the left elytron in the right elytron fixed reference system.


In some beetles with extremely curved trajectories of divergence, the sutural lock is adopted to rotation during unlocking:

Profile of the sutural locking structure in a cetoniid Rhomborhina unicolor .

Continuation of this research see in
Double rotation of the opening (closing) elytra in beetles (Coleoptera)


Collection of films:

Courtship dances in a fly, Lispe spp.

Stick friction in a lantern fly, Lycorma delicatula

Arolium of a hornet, Vespa crabro

Indirect closing of elytra in a cockchafer, Melolontha

Righting kinematics in beetles (Insecta: Coleoptera)

Leg coordination during turning on an extremely narrow substrate in a bug, Mesocerus marginatus (Heteroptera, Coreidae)

Swimming in the Diving Wasp Prestwichia aquatica (Hymenoptera: Trichogrammatidae)

Kinematics of elytra in beetles

Indirect closing of elytra in various beetles

Double rotation of the opening (closing) elytra in beetles (Coleoptera)

Actuation and performance of the elytron-to-body articulation in a diving beetle


I. I. Schmalhausen Institute of Zoology, 2004-2009