Mechanical and optical properties of the femoral chordotonal organ in beetles (Coleoptera).

The femoral chordotonal organ (FCO) in beetles differs from that in orthopterids in the origin of its apodeme: it originates directly from the tibia in the latter, but amidst the tendon of the extensor muscle in the former. In many beetles, the apodeme pops up from the tendon as a short sclerite (arculum). It turns distally upon bending of the tibia. The turn of the arculum is several times more than the turn of the tibia, and the arculum is connected to the FCO. This system behaves as a high-pass filter with a time constant close to the step period. Various aspects of the arculum have been studied previously, including its shape in various taxa, its biomechanics, matched neural activity in the FCO, as well as evolutionary aspects. The results of previous studies, published in 1985-2003 in Russian, are inaccessible to most foreign readers. However, original texts and the list of studied species (>350) are now available online. Recently, we minimized the system to three components: the proximal tibial ledge, the tendon and the arculum. The elastic tendon contains resilin. In four model species, the arculum readily turned upon stretching of the tendon. Turning was video recorded. The force of approximately 0.005 N, applied to a tendon approximately 0.25 mm in size, is enough for the utmost turn of the arculum. The arculum turned also upon local deformations close to its base. The ability to turn vanished after incision between the arculum and the distal part of the extensor apodeme. A mechanical model of an amplifier is proposed. The apodeme includes optically active structures, which behave differently in polarized light.

Indirect closing of the elytra in a cockchafer, Melolontha hippocastani F. (Coleoptera: Scarabaeidae).

Actuation of the closing of the elytra was previously ascribed to intrinsic muscles in the mesothorax. We investigated closing (1) by loading or arrest of some thoracic segments in a tethered flying beetle, (2) by animation, i.e. passive motion of preparations of the thorax simulating the action of some muscle, and (3) by excision of some parts of sclerites or cuts across certain muscles. We found out that depression of the prothorax, necessary to unlock the elytra, precedes their opening but elevation of the prothorax is synchronous with the closing. The closing is retarded if the elevation is retarded by loading; if the elevating prothorax is clamped, then the closing is also arrested or hindered; animation of the elevation of the prothorax in the dead animal is enough for the closing of the previously spread elytra; the closing is prevented if a piece at the hind edge of the pronotum, positioned in front of the root of an elytron, is excised. This excision also prevents closing in the in vivo experiments. Mechanical interaction between the elytron and the prothorax is limited to the contact point between the posterior edge of the pronotum and the lateral apophysis of the root. Thus, the elevation of the prothorax is the indirect and main mechanism of the closing in Melolontha.

Adhesive properties of the arolium of a lantern-fly, Lycorma delicatula (Auchenorrhyncha, Fulgoridae).

The arolium in Lycorma delicatula is shaped as a truncated pyramid, tapering proximally. The base or the terminal area is corrugated, forming parasagittal wrinkles (period 1.5-5.0 microm), which are supported from inside by cuticular dendrites. Side faces of the arolium are made up of sclerotized dorsolateral plates. When claws slip on a smooth substrate and pronate, the dorsolateral plates diverge and expand the sticky terminal area. The real contact area with the glass plate was recognized by light reflection on its periphery. This area was measured and shown to be smaller when the leg was pressed perpendicularly to the substrate (0.02 mm(2)) than when it was sheared in a direction parallel to the substrate (0.05 mm(2)). Attachment forces were measured with the aid of dynamometric platforms during pulling of active insects from horizontal or vertical glass surfaces. Normal adhesive force (about 9-12 mN) was much less than friction force during sliding with velocity of 6-17 mm/s (50-100 mN); however, when expressed in tenacity per unit contact area the difference was less pronounced: 170 and 375-625 mN/mm(2), respectively. Sliding of the arolium during shear displacement was shown to be oscillatory in frame-by-frame video analysis. Relaxative oscillations consisted of periodical sticks-slips of the arolium along the glass surface.

Leg deformation during imaginal ecdysis in the downy emerald, Cordulia aenea (Odonata, Corduliidae).

A dragonfly larva migrates from the water to the shore, perches on a plant stem and grasps it with strongly flexed legs. Adult legs inside the larval exoskeleton fit to the larval legs joint-to-joint. The adult emerges with stretched legs. During the molt, an imaginal leg must follow all the angles in exuvial joints. In turn, larval apodemes are withdrawn from imaginal legs. We visualized transient shapes of the imaginal legs by the instant fixation of insects at different moments of the molt, photographed isolated exuvial legs with the imaginal legs inside and then removed the exuvial sheath. Instant shapes of the imaginal tibia show sharp intrapodomere bends copying the angle in the larval femoro-tibial joint. The site of bending shifts distad during the molt. This is possible if the imaginal leg is pliable. The same problem of leg squeezing is also common in hemimetabolous insects as well as in other arthropods, whereas holometabolous insects overcome problems of a tight confinement either by using leg pliability in other ways but not squeezing (cyclorrhaphan flies, mosquitoes) or by pulling hardened legs out without change of their pupal zigzag configuration (moths, ants, honey bees). The pupal legs are not intended to grasp any external substrate.

Transient leg deformations during eclosion out of a tight confinement: A comparative study on seven species of flies, moths, ants and bees.

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 Formica 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.

A Houdini's trick in a fly: Leg unfolding with the aid of transient hinges in an extricating Calliphora vicina (Diptera: Calliphoridae).

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 2-3 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 - 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.

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

The turning movement of a bug, Mesocerus marginatus, is observed when it walks upside-down below a horizontal beam and, at the end of the beam, performs a sharp turn by 180 degrees . The turn at the end of the beam is accomplished in three to five steps, without strong temporal coordination among legs. During the stance, leg endpoints (tarsi) run through rounded trajectories, rotating to the same side in all legs. During certain phases of the turn, a leg is strongly depressed and the tarsus crosses the midline. Swing movements rotate to the same side as do leg endpoints in stance, in strong contrast to the typical swing movements found in turns or straight walk on a flat surface. Terminal location is found after the search through a trajectory that first moves away from the body and then loops back to find substrate. When a leg during stance has crossed the midline, in the following swing movement the leg may move even stronger on the contralateral side, i.e. is stronger depressed, in contrast to swing movements in normal walking, where the leg is elevated. These results suggest that the animals apply a different control strategy compared to walking and turning on a flat surface.

Lehr's fields of campaniform sensilla in beetles (Coleoptera): functional morphology. III. Modification of elytral mobility or shape in flying beetles.

Some flying beetles have peculiar functional properties of their elytra, if compared with the vast majority of beetles. A "typical" beetle covers its pterothorax and the abdomen from above with closed elytra and links closed elytra together along the sutural edges. In the open state during flight, the sutural edges diverge much more than by 90°. Several beetles of unrelated taxa spread wings through lateral incisions on the elytra and turn the elytron during opening about 10-12° (Cetoniini, Scarabaeus, Gymnopleurus) or elevate their elytra without partition (Sisyphus, Tragocerus). The number of campaniform sensilla in their elytral sensory field is diminished in comparison with beetles of closely related taxa lacking that incision. Elytra are very short in rove beetles and in long-horn beetles Necydalini. The abundance of sensilla in brachyelytrous long-horn beetles Necydalini does not decrease in comparison with macroelytrous Cerambycinae. Strong reduction of the sensory field was found in brachyelytrous Staphylinidae. Lastly, there are beetles lacking the linkage of the elytra down the sutural edge (stenoelytry). Effects of stenoelytry were also not uniform: Oedemera and flying Meloidae have the normal amount of sensilla with respect to their body size, whereas the sensory field in the stenoelytrous Eulosia bombyliformis is 5-6 times less than in chafers of the same size but with normally linking broad elytra.

Lehr's fields of campaniform sensilla in beetles (Coleoptera): functional morphology. II. Wing reduction and the sensory field.

Loss of the flight ability and wing reduction has been reported for many taxa of Coleoptera. If elytra are closed, their roots are clenched between the tergum and the pleuron, forces applied to the elytra can not be transmitted to the field of campaniform sensilla situated on the root. That is why it is plausible to assume that the field becomes redundant in non-flying beetles. We examined the relationships between the hind wing reduction and characters of this mechanosensory field in beetles of six families. We measured the size of the elytron, that of the hind wing and counted the number of sensilla in the sensory field. Mesopterous non-flying beetles retain one half to one third of sensilla present in macropterous species of the same body size. Further reduction of the sensory field in brachypterous species is obvious, but sensilla are still present in insects with strongly reduced wings, as long as their elytra are separable and mesothoracic axillaries are present. Complete loss of sensilla coincides with the existence of a permanent sutural lock. However, some beetles with permanently locked elytra and absence of axillaries still retain few campaniform sensilla. A very special case of an extreme wing modification in feather-wing beetles is considered. No sensilla were revealed either on the root of the elytron or on the basal segment of such fringed wings in flying ptiliid species.

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

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. 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.

Lehr's fields of campaniform sensilla in beetles (Coleoptera): functional morphology. I. General part and allometry.

In this first of three articles we show the construction of the articular part of the elytron, the root. The root bears a conspicuous field of campaniform sensilla. This field was studied using light and scanning electron microscopes. The diversity of shape of the field among beetles, types of orientation of elongated sensilla within the field, individual variability of their number among conspecifics are demonstrated. Elongated sensilla point to the junction of the elytron with the second axillary plate. Presumably, they monitor twist movement in this junction, which is possible if the elytron is open. The goal of the whole project is to reveal the effect of both structure and function of the hind wings and elytra on the morphology of this mechanosensory field. Our data on allometric relationships between the animal size and quantitative characteristics of the field in normally flying beetles provide an important background for further functional analysis of this sensory organ. We selected 14 series of several species belonging to the same taxon but differing in size from big to small. It is revealed that the area of the sensory field is directly proportional to the elytral area, whereas the number of sensilla is proportional to the square root of the elytral area. Despite the great range in the elytral area (1500 times) in series of selected species the area of an external pit or cap of a single sensillum varies only 25-fold. The density of sensilla per unit area of the sensory field increases with decrease of the elytral area.

Experimental evidence on actuation and performance of the elytron-to-body articulation in a diving beetle, Cybister laterimarginalis (Coleoptera, Dytiscidae).

Movements of the elytra and axillary sclerites were video recorded in tethered flying beetles and in manipulated mounts. Mesothoracic axillary plates are homologues of those in the metathorax. Two anterior axillaries (Ax1, Ax2) fuse together; they are hinged to the third axillary plate (Ax3). In turn, Ax3 is hinged with the elytron. During takeoff, a beetle abducts and highly elevates its elytra (1), then droops the elytra in a flatly spread position (2); closing is adduction in a horizontal plane (3). These steps have been simulated: (1) by pressing down the anterior horn; (2) occurred spontaneously after release of pressing; (3) the elytron closed flatly either by manual turn of the elytron or by manual elevation of the prothorax. Anterior axillaries rotated forward and down during (1), returned during (2) and remained immobile during closing. Ax3 is folded between the closed elytron and Ax1+Ax2; it unfolds during opening. Two hinges of Ax3 form a Z-configuration and provide a linked drive for complicated rotation of the elytron. Opening was impaired in vivo if tergal leg protractor and depressor were disabled, closing did not suffer. Closing was prevented by excision in the hind edge of the pronotum, not harmful for opening. Role of direct and indirect muscles in transient elytral movements is discussed.

Indirect closing of elytra by the prothorax in beetles (Coleoptera): general observations and exceptions.

Voluntary movements of the prothorax and the elytra in tethered flying beetles and manually induced movements of these parts in fresh dead beetles were recorded in 30 species representing 14 families. Participation of prothoracic elevation in the closing of the elytra was demonstrated in three ways. (i) The elevation was always simultaneous with elytral closing, in contrast to depression and elytral opening; a rare exception occurred in Lucanus cervus, whose elytra sometimes started to close before the cessation of wing strokes and the elevation of the prothorax. (ii) The manipulated elevation always induced closing of the spread elytra; the mechanical interaction between the hind edge of the pronotum and the roots of the elytra is a universal mechanism of closing the elytra in beetles. (iii) The prevention of pronoto-elytral contact in live beetles by the excision of the hind edge of the pronotum in front of the root prevented elytral closing after normal flight. Exceptions to this rule included some beetles that were able to close their elytra after such an excision: tiger beetles and diving beetles (seldomly) and rose chafers (always). This ability in Adephaga may be explained by attachments of the muscle actuating the 4th axillary plate, which differ from the attachments in Polyphaga. Cetoniinae open their elytra only by a small amount. It is proposed that their small direct adductors in combination with the elasticity of the sclerites are enough to achieve elytral closing without additional help from the prothorax.

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

Transient movements of the elytra (opening and closing) were filmed in beetles tethered from below. A total of 39 specimens of 18 species representing 11 families were examined. Bright markers glued to the elytra were traced frame by frame. Body-fixed 3D traces of apical and shoulder markers were reconstructed. Shapes of traces reflected different steps of elytral movement and different types of flight. Flat circular arcs were fitted to scattered traces using the least square method. The rotation axis of the apical marker was always directed at the contralateral side. The trace of the shoulder marker was, as a rule, non-parallel to the apical trace. Usually, the shoulder marker on the costal edge of the elytron uniformly supinated in the course of adduction of the apical marker. Traces of opening and closing coincided, hence the double rotation of the elytron had one degree of freedom. The elytron to body articulation in beetles is, presumably, a spherical mechanism with two separate but linked drives for a broad swing during opening (closing).

Gimbals in the insect leg.

We studied the common kinematic features of the coxa and trochanter in cursorial and raptorial legs, which are the short size of the podomers, predominantly monoaxial joints, and the approximate orthogonality of adjacent joint axes. The chain coxa-trochanter with its short elements and serial orthogonality of joint axes resembles the gimbals which combine versatility and tolerance to external perturbations. The geometry of legs was studied in 23 insect species of 12 orders. Insects with monoaxial joints were selected. The joint between the trochanter and the femur (TFJ) is defined either by two vestigial condyles or by a straight anterior hinge. Direction of the joint axes in the two basal podomers was assessed by 3D measurements or by goniometry in two planes. Length of the coxa is <15% (mostly <8%) of the total length of the cursorial leg, that of the trochanter <10%. Angles between the proximal and distal joint axes in the middle coxa range from 124 to 84 degrees (mean 97+/-14 degrees ), in the trochanter (in all legs studied) from 125 to 72 degrees (mean 90+/-13 degrees ). Vectors of the distal axis in the coxa are concentrated about the normal to the plane defined by the proximal axis and the midpoint between the distal condyles. These vectors in the trochanter lie at various angles to the normal; angles are correlated with the direction of the TFJ relative to the femur. Range of reduction about the TFJ is over 60 degrees in the foreleg of Ranatra linearis, Mantispa lobata and the hind leg in Carabus coriaceus (confirming observations of previous authors), 40-60 degrees in the foreleg of Vespa crabro and in the middle one in Ammophila campestris, 10-30 degrees in other studied specimens. The special role of the trochanter in autotomy and in active propulsion in some insect groups is discussed. The majority of insects possess small trochanters and slightly movable TFJs with the joint axis laying in the femur-tibia plane. We pose the hypothesis that the TFJ damps external forces, the vectors of which lie off the femur-tibia plane, the reductor muscle acting as a spring. Thus the TFJ contributes to dynamic stability of legged locomotion.

Courtship dances in the flies of the genus Lispe (Diptera: Muscidae): from the fly's viewpoint.

Two predatory fly species, Lispe consanguinea Loew, 1858 and L. tentaculata DeGeer, 1776, inhabit the supralittoral zone at the shore of a fresh-water reservoir. Both species look alike and possess similar "badges," reflective concave silvery scales on the face. Flies occupy different lek habitats. Males of the first species patrol the bare wet sand on the beach just above the surf. Males of the second species reside on the more textured heaps of algae and stones. Courtship and aggressive behaviour of males was video-recorded and analysed frame by frame. Visual stimuli provided by the conspecific partner were computed in the body-fixed space of a fly observer. Males of L. consanguinea perform long pedestrian dances of pendulating circular arcs (frequency 2 s(-1), median radius 2.5 cm, linear velocity 0.130 m/s). Right and left side runs are equally probable. Circular runs are interrupted by standby intervals of average duration 0.35 s. The female views the male as a target covering 2 by 2 ommatidia, moving abruptly with the angular velocity over 200 degrees/s in a horizontal direction down the path of about 50 degrees till the next standpoint. Dancing is evenly distributed around the female. On the contrary, the male fixates the image of the female within the narrow front sector (median +/-10 degrees); the target in his view has 6-7 times less angular velocity and angular span of oscillations, and its image in profile overlays 6-8 by 2 ommatidia. If the female walks, the male combines tracking with voluntary circular dances. Rival males circle about one another at a distance shorter than 15 mm, but not in close contact. Males of L. tentaculata are capable of similar circular courting dances, but do so rarely. Usually they try to mount any partner immediately. In the latter species, male combat consists of fierce wrestling. Flies of both species often walk sideward and observe the partner not in front but at the side.

Geometry of elytra opening and closing in some beetles (Coleoptera, Polyphaga).

Elytra in beetles move actively, driven by their own muscles, only during transient opening and closing. The kinematics of these movements have been inadequately described, sometimes controversially. Our goal was a quantitative 3-D description of diverse active movements of the elytra, in terms of directions of the axes of elytra rotation. Broad opening and closing was video recorded in beetles, tethered by the mesothorax, and has been analyzed frame by frame. For tracing, small dots or straw arms were 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 backwards in Chalcophora mariana. In Cetonia aurata, the AAA had a 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) occurred. 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 degrees) and partition to the sides, combined with an inward turn (<2-3 degrees). 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.

Righting kinematics in beetles (Insecta: Coleoptera).

Twenty modes of stereotyped righting motions were observed in 116 representative species of coleoptera. Methods included cine and stereocine recording with further frame by frame analysis, stereogrammetry, inverse kinematic reconstruction of joint angles, stroboscopic photography, recording of electromyograms, 3D measurements of the articulations, etc. The basic mode consists of a search phase, ending up with grasping the substrate, and a righting, overturning phase. Leg coordination within the search cycle differs from the walking cycle with respect to phasing of certain muscle groups. Search movements of all legs appear chaotic, but the tendency to move in antiphase is still present in adjacent ipsilateral and contralateral leg pairs. The system of leg coordination might be split: legs of one side might search, while contralateral legs walk, or fore and middle legs walk while hind legs search. Elaborated types of righting include somersaults with the aid of contralateral or diagonal legs, pitch on elytra, jumps with previous energy storage with the aid of unbending between thoracic segments (well-known for Elateridae), or quick folding of elytra (originally described in Histeridae). Righting in beetles is compared with righting modes known in locusts and cockroaches. Search in a righting beetle is directed dorsad, while a walking insect searches for the ground downwards. Main righting modes were schematized for possible application to robotics.

The coxal articulation of the insect striking leg: A comparative study.

The thoraco-coxal muscles and the geometry of the leg suspension inside the prothorax were investigated in a praying mantis Mantis religiosa, an aquatic bug Ranatra linearis, and a neuropterid Mantispa lobata. Comparative observations were carried out on a cockroach Nauphoeta cinerea, a pentatomid bug Graphosoma italicum and a neuropterid Creoleon plumbeus. Adaptation of the thoraco-coxal joint to striking function was attained by different morphological structures, preadapted specifically in each insect order with respect to the articulation of the coxa, the number of muscles and the development of the endoskeleton. Adaptation provides for two main properties: maximal distance of the strike and the required rigidity of the supporting structures. In turn, these goals have given rise to some secondary problems, e.g., the versatility of the thoraco-coxal joint and the supposed coactivation of different muscle groups during the strike. J. Morphol. 236:127-138, 1998. © 1998 Wiley-Liss, Inc.

Structure and mechanics of the tarsal chain in the hornet, Vespa crabro (Hymenoptera: Vespidae): implications on the attachment mechanism.

Two combined mechanisms on the hornet tarsus are adapted to attachment to the substrate: a friction-based (claws and spines) and an adhesion-based one (arolium). There are two ranges of substrate roughness optimal for attachment, either very smooth or very rough. There is an intermediate range of substrate grains of small but non-zero size, where both of these mechanisms fail. The optimal size of substrate grains for hornet grasping was 50-100 microm. Maximal hold to the substrate was achieved when surface irregularities were clamped between the claws of opposite legs. In such a position, the insect could withstand an external force which was almost 25 times larger than its own weight. The tarsal chain is an important part of the entire attachment mechanism. The articulations in the kinematic chain of tibia-tarsus-pretarsus are monocondylar. Three tarsal muscles and one head of the claw retractor muscle originate in the tibia. On pull to the retractor tendon, the tarsus bends in a plane. All elements of the tarsal kinematic chain have one active degree of freedom. The distance between the intertarsomeric articulation point and the tendon of the claw retractor (75-194 microm) corresponds to an efficiency of 1 degrees per 1-3 mircom of pulling distance travelled by the tendon. The claw turns about 1 degrees per 4.3-5.0 microm of pulling distance travelled by the unguitractor. The arolium turns forward and downward simultaneously with flexion of the claws. The kinematic chain of the arolium lacks real condylar joints except the joint at the base of the manubrium. Other components are tied by flexible transmissions of the membranous cuticle. The walking hornet rests on distal tarsomeres of extended tarsi. If the retractor tendon inside the tarsus is fixed, passive extension of the tarsomeres might be replaced by claw flexion. Tarsal chain rigidity, measured with the force tester, increased when the retractor tendon was tightened. Probably, pull to the tendon compresses the tarsomeres, increasing friction within contacting areas of rippled surfaces surrounding condyles within articulations.