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< Leonid I. Frantsevich >

Leonid Frantsevich and Stanislav Gorb

Arcus as a tensegrity structure in the arolium of wasps (Hymenoptera: Vespidae)

Zoology 2002, 105: 225–237

Summary. The unfolding of the hymenopteran attachment pad (arolium) may be achieved in two ways, hydraulic and mechanical. The first was confirmed in experiments with pressure applied to more proximal leg parts and on immersion in hypotonic solutions. Presumably, this way of unfolding does not play an important role for a living hornet, Vespa crabro. Mechanical unfolding was studied experimentally with the aid of a micromanipulator pulling the tendon of the musculus retractor unguis. Ablation experiments on different parts of the arolium indicated that the arcus is the most crucial element for mechanical unfolding. The shape of the arcus in closed and open conditions was measured using a 3D measurement microscope and reconstructed by means of 3D computer graphics. The arcus coils up upon being freed from the arolium tissues, and coils up even more after immersion into a 10% aqueous solution of NaOH. Geometrical models of the arcus are proposed, from which the rotational moment of elasticity is derived. Conformations and deformations of the arcus are quantified in order to explain its role in the folding and unfolding processes of the arolium. The diversity of approaches supports the idea that the arcus is a prestressed (tensegrity) structure providing immediate, soft, and graded transmission of forces during folding and unfolding action of the arolium.

Autocoiling of arci extracted from arolium tissues, supercoiling
after treatment with 10% NaOH-solution, and computer models of coils.

Passive spreading of the arolium of Vespa crabro by
displacement of the retractor unguis tendon
(click on the image to view the movie)

Hydraulic spreading of the arolium of Vespa crabro by
pressure applied to the terminal tarsomere.
(click on the image to view the movie)

Unhappy attempts to release the arolium attached to
the glass surface.
(click on the image to view the movie)


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