Insect walking techniques on thin stems

Abstract

The attachment ability of insects on surfaces are associated not only with the micro-and nanostructure of the adhering part of an attachment device, but also with the global scale kinematics responsible for contact formation and release. In the present study, the locomotory techniques of several representatives of insects from four different orders (Orthoptera, Heteroptera, Coleoptera, and Hymenoptera), possessing different types of attachment structures, are described. The study is based on video recordings of insects walking on a flat surface and on cylindrical rods of various thickness, imitating plant stems. Attachment devices of tarsi and pretarsi were visualized using Scanning Electron Microscopy. The results show a different manner in the use of adhesive structures on substrates with various curvatures. Insects bearing attachment pads on proximal tarsomeres usually touch flat and curved substrates using all tarsomeres, whereas insects with their attachment devices on the distal tarsomeres usually walk on flat surfaces using the distal tarsomeres of the overextended tarsus. On substrates, with diameters comparable to or larger than the tarsus length, insects walk above the stem by clasping the stem with the bent tarsi. On thin stems, insects clasp the stem between their tarsi and hang under the stem. Thus, on thin and thick rods, forces applied to attachment organs act in opposite directions. There are two methods of leg positioning for walking on a rough flat substrate. In the first case, the tarsus is straightened and the rough substrate is gripped between the claws and the proximal complex of attachment devices (tarsal euplantulae, fossulae spongiosa, and terminal spurs of tibiae). In the second case the tibia does not touch the substrate; the insect is supported only by distal tarsomeres. The tarsus is in an overextended condition. On rods, with diameters comparable to or larger than the tarsus length, insects walk by clasping the stem with the bent tarsi. This posture is characteristic for the majority of insects independent of the tarsal position they normally use while walking on a plane. If the rod's diameter is smaller than the tarsus length, walking insects usually clutch it between contralateral tarsi. Using such a posture they are supported by interlocking or by strong friction, generated by attachment devices of the proximal tarsomeres, and do not use attachment devices of the pretarsus. Contact with the substrate is reinforced due to the coordinated contralateral clutch using all supporting legs. It is concluded that the use of different types of attachment structures correlates with locomotory techniques.

Level locomotion in wood ants: evidence for grounded running

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“…The first mechanism is generated by rigid claws interacting with surface irregularities of macroscopically rough substrates [3]; the second involves adhesive pads, including hairy adhesive structures and smooth flexible pads, to maximize the contact area and guarantee the acquisition of attachment force on smooth surfaces [4]. It has been previously demonstrated that insects can stand or move on vertical substrates using their claws to generate mechanical interlock, when the diameter of macroscopic surface irregularities is much larger than the diameter of the claw tip [5][6][7]. In this case, insects generally use the surface irregularities as solid anchorage points for their claws to grasp.…”

How a lack of choice can force ants to climb up waxy plant stems

“…For ants, most of which rely on the food sources located on plants, reliable locomotion is only possible through the presence of elaborate adhesive systems (Wojtusiak et al 1995;Federle et al 2000Federle et al , 2002Orivel et al 2001;Federle and Endlein 2004;Gladun and Gorb 2007). Previous studies have demonstrated impressive adhesive capability of some ant species.…”