Arthropod touch reception: stimulus transformation and finite element model of spider tactile hairs

Striving towards an in depth understanding of stimulus transformation in ar thropod tactile hairs, we studied the mechanical events associated with tac tile stimulation. A finite element model was developed taking a tarsal tact ile hair of the spider Cupiennius salei as an example. Considering hair dia meter, wall thickness, and curvature, the hair is subdivided into six regio ns each with its specific mechanical properties. When the hair is touched f rom above with a flat surface oriented parallel to the tarsus the point of stimulus contact moves towards the hair base with increasing load and hair deflection. Thereby the effective lever arm is reduced protecting the hair against breaking near its base. At the same time the mechanical working ran ge of the hair increases implying higher mechanical sensitivity for small d eflections (about 5x10(-5) N/degrees) than for large deflections (about 1x1 0(-4) N/degrees). The major stresses within the hair shaft are axial stress es due to bending. The position of stress maxima moves along the shaft with the movement of the stimulus contact point. Remarkably, the amplitude of t his maximum (about 1x10(5) N/m(2)) hardly changes with increasing loading f orce due to the way the hair shaft is deflected by the stimulus.