A comparison of tarsal morphology and traction force in the two burying beetles Nicrophorus nepalensis and Nicrophorus vespilloides (Coleoptera, Silphidae)

Abstract

Our aim was to compare friction and traction forces between two burying beetle species of the genus Nicrophorus exhibiting different attachment abilities during climbing. Specifically, the interaction of adhesive hairs and claws during attachment with respect to various surface properties was investigated by using a 2 × 3 experimental design. Traction force was measured for two different surface energies (hydrophilic vs hydrophobic) varying in roughness from smooth to micro-rough to rough. Nanotribometric tests on single legs were also performed. The external morphology of the attachment devices investigated by scanning electron microscopy suggested higher intra-specific (intersexual) than inter-specific differences. Whereas differences between the two species in traction force were high on smooth surfaces, no differences could be detected between males and females within each species. With claws intact, both species showed the highest forces on rough surfaces, although N. nepalensis with clipped claws performed best on a smooth surface. However, N. nepalensis beetles outperformed N. vespilloides, which showed no differences between smooth and rough surfaces with clipped claws. Both species demonstrated poor traction forces on micro-rough surfaces. Results concerning the impact of surface polarity were inconclusive, whereas roughness more strongly affected the attachment performance in both species. Nanotribometric analyses of the fore tarsi performed on micro-rough and rough surfaces revealed higher friction in the proximal (pull) direction compared with the distal (push) direction. In these experiments, we detected neither differences in friction performance between the two species, nor clear trends concerning the influence of surface polarity. We conclude that the investigated morphological traits are not critical for the observed interspecific difference in attachment ability on smooth surfaces. Furthermore, interspecific differences in performance are only clear on smooth surfaces and vanish on micro-rough and rough surfaces. Our results suggest that even subtle differences in the adhesion-mediating secretion in closely related species might result in qualitative performance shifts.

Interaction of a non-axisymmetric artificial single spatula with rough surfaces

“…For Seta-II (figure 1 b ), the seta was developed as a square column with a uniform cross-section to facilitate manufacture. The design of the spatula was influenced by the spatula-like structure of insects, where the seta is smoothly attached to the spatula [31]. Furthermore, the transitional characteristics of the joints resulted in an augmentation of the spatula’s thickness, which was arranged from 100 nm at the proximal end to 10 nm at the distal end.…”

The tight attachment achieved by the male discoidal setae is possibly a counter-adaptation to the grease layer on female integument surfaces in green dock beetles

“…Considering that attachment organs for locomotion are one of the most essential interfaces between organisms and their environment, the evolution of these organs was crucial for many arthropods that prowl or crawl on various substrata. The tip shape of these fibrillar structures is diverse among species and even within a single attachment pad [4,[6][7][8], resulting in a wide variety of terrestrial and aquatic surfaces that animals can walk on and adhere to.…”

“…Owing to this effect, the grease layer on the female body surface could reduce tarsal adhesion [12,24,25]. Moreover, stiffness, chemistry, texture and humidity of substrates are also known to influence attachment forces [7,9,[26][27][28][29][30][31][32][33][34][35][36][37]. Until now, these effects have been well studied on artificial flat smooth and rough surfaces, but rarely in the context of copulation that never occurs on flat surfaces.…”

Smooth and slipless walking mechanism inspired by the open–close cycle of a beetle claw

“…Many insects have claws and/or hairy or smooth attachment pads, which they use to walk stably [1][2][3][4][5]. In particular, the ability to attach to surfaces using attachment pads has been investigated in many insects, including stick insects [3,[6][7][8][9][10], beetles [4,[11][12][13][14][15], cockroaches [16][17][18][19], and flies [20,21]. These investigations have found that similar to geckos', insects' attachment pads generate significant van der Waals forces [22][23][24][25][26][27][28][29][30][31].…”