Rate-dependent adhesion in combination with the collaborative action of limbs facilitates grasshoppers’ reliable attachment under highly dynamic conditions

Description

Dynamic attachment is essential for animals to cope with unexpected disturbances. Minor attention has been paid to the dynamic performance of the individual adhesive pads. However, the whole-animal results are even more informative for understanding animal attachment intelligence. In this article, we tested grasshoppers by pulling them off at different speeds on a glass rod. Surprisingly, the feet did not always maintain contact with the rod but released when the legs were extended and tried to reconnect rapidly with the surface. This type of adjustment may effectively reduce the impact on the pads and their potential damage. As we increased the pulling speeds from 1 mm/s to 400 mm/s, the maximum forces of insects with a single front tarsus and insects with entire tarsi were almost proportional to the 1/3 power of pulling speeds by 0.11 times and 0.29 times, respectively. In extreme cases, the force was even 800 times greater than the weight of the insects, which is an extremely high performance for the smooth insect pads. This work not only helps us to understand the dynamic attachment of the animal as a whole but also enriches our knowledge of animal attachment in extreme situations.

Steps to reproduce

Grasshoppers (Oxya chinensis, body mass 0.1-1.0g, snout-event length LSV: 2-4cm) captured at Purple Mountain (Nanjing, China) were glued with their dorsal thorax surface to a thin stem, which was subsequently linked to a multi-axis force transducer19. A glass rod (diameter 6mm) was used to mimic convex substrates typical for the habitat of this animal. The substrate was attached to a two-dimensional mobile platform to control its displacement and velocity (Fig.1). The glass rod was first brought towards the animal until its thorax came into contact with it. The stem connecting the insects and the force sensor has a high respect ratio (300), resulting in a low radial stiffness. After touching the glass rod, the insects could freely move their limbs and modify their positions. After several seconds given for the insects to establish an initial contact, we moved the rod away from the animal at different speeds (1mm/s, 10mm/s, 50mm/s, 100mm/s, 200mm/s, 300mm/s or 400mm/s), then collected the force signals through an NI DAQ model (NI 9237, USA) at a rate of 1662 - 5000 Hz and monitored the motion by a high-speed camera (BFS-U3-16S2M-CS, FLIR Systems Inc., USA) at 500fps. At first, eighteen grasshoppers with intact tarsi and 12 grasshoppers with a single front tarsus were tested. Notably, four individuals were tested in both cases. The insects with a single tarsus were allowed to rest for at least 48 hours after the surgery. The rod was cleaned using 75% alcohol before each test to minimise the effects of secretion stains from the insect’s pads.

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