Arthropod Cuticular Hairs: Tactile Sensors and the Refinement of Stimulus Transformation

Abstract

Arthropods are richly supplied with mechanosensitive cuticular hairs. Much of the refinement of these sensors including their specificity and their sometimes exquisite sensitivity lies in the mechanical processes characterizing the uptake and transformation of their adequate stimulus. In order to understand these processes the application of approaches used in engineering is highly rewarding. In this chapter we report on micromechanical measurements and the application of Finite Element analysis to spider tactile hairs after first contrasting these with hairs responding to airflow. The most relevant mechanical difference between these two types of hairlike sensors is the stiffness of their articulation, which is larger by about four powers of ten in tactile hairs. As a consequence tactile hairs are not only deflected but in addition bent by the stimulus. Their actual bending is dominated by the modulus of elasticity of the hair shaft and the second moment of area and its changes along the hair. The spider tactile hairs examined perfectly combine high sensitivity (threshold deflection by torques measuring ca. 5 × 10−10 Nm) with efficient protection from being overloaded. They may be classified as lightweight structures of equal maximum strength, representing sophisticated micro-electromechanical systems.