Centre for Cell Engineering, University of Glasgow, Joseph Black Building, University Avenue, Glasgow, UK.
Proc Biol Sci. 2013 Feb 27;280(1757):20122868. doi: 10.1098/rspb.2012.2868. Print 2013 Apr 22.
Many insects possess adhesive organs that can produce extreme attachment forces of more than 100 times body weight but they can rapidly release adhesion to allow locomotion. During walking, weaver ants (Oecophylla smaragdina) use only a fraction of their maximally available contact area, even upside-down on a smooth surface. To test whether the reduced contact area makes the ants more susceptible to sudden and unexpected detachment forces, for example, by rain or wind gusts, we investigated the reaction of untethered ants to rapid horizontal displacements of the substrate. High-speed video recordings revealed that the pad's contact area could more than double within the first millisecond after the perturbation. This contact area expansion is much faster than any neuromuscular reflex and therefore represents a passive 'preflex', resulting from the mechanical properties and geometrical arrangement of the (pre-)tarsus. This preflex reaction protects ants effectively against unexpected detachment, and allows them to use less contact area during locomotion. Contact area expanded most strongly when the substrate displacement generated a pull along the axis of the tarsus, showing that the ants' preflex is direction-dependent. The preflex may be based on the ability of Hymenopteran adhesive pads to unfold when pulled towards the body. We tested Indian stick insects (Carausius morosus), which have smooth pads that lack this motility. Similar to the ants, they showed a rapid and direction-dependent expansion of the contact area mainly in the lateral direction. We propose that the preflex reaction in stick insects is based on the reorientation of internal cuticle fibrils in a constant-volume system, whereas the ants' pad cuticle is probably not a hydrostat, and pad extension is achieved by the arcus, an endoscelerite of the arolium.
许多昆虫都具有粘性器官，可以产生超过 100 倍体重的极端附着力，但它们可以迅速释放附着，从而允许运动。在行走过程中，织叶蚁（Oecophylla smaragdina）即使在光滑的表面上倒立，也只使用其最大可用接触面积的一小部分。为了测试减少的接触面积是否会使蚂蚁更容易受到突然和意外的分离力的影响，例如雨水或阵风，我们研究了未系绳的蚂蚁对基质快速水平位移的反应。高速视频记录显示，在干扰后的第一毫秒内，垫的接触面积可以增加一倍以上。这种接触面积的扩展速度远快于任何神经肌肉反射，因此代表了一种被动的“预反射”，这是由（预）跗节的机械特性和几何排列产生的。这种预反射反应有效地保护蚂蚁免受意外分离的影响，并使它们在运动中使用更少的接触面积。当基质位移沿跗节的轴产生拉力时，接触面积的扩展最为强烈，这表明蚂蚁的预反射是有方向依赖性的。预反射可能基于膜翅目粘性垫在向身体方向拉动时展开的能力。我们测试了光滑垫缺乏这种运动能力的印度竹节虫（Carausius morosus）。与蚂蚁类似，它们的接触面积主要在横向迅速且有方向依赖性地扩展。我们提出，竹节虫的预反射反应基于在体积恒定的系统中内部角质纤维的重新定向，而蚂蚁的垫角质可能不是静水力学的，垫扩展是通过弓来实现的，弓是 arolium 的内骨。
