Living organisms use composite materials for various functions, such as mechanical support, protection, motility and the sensing of signals. Although the individual components of these materials may have poor mechanical qualities, they form composites of polymers and minerals with a remarkable variety of functional properties. Researchers are now using these natural systems as models for artificial mechanosensors and actuators, through studying both natural structures and their interactions with the environment. In addition to inspiring the design of new materials, analysis of natural structures on this basis can provide insight into evolutionary constraints on structure-function relationships in living organisms and the variety of structural solutions that emerged from these constraints.

Spiders mainly feed on insects. This means that their fangs, which are used to inject venom into the prey, have to puncture the insect cuticle that is essentially made of the same material, a chitin‐protein composite, as the fangs themselves. Here a series of structural modifications in the fangs of the wandering spider Cupiennius salei are reported, including texture variation in chitin orientation and arrangement, gradients in protein composition, and selective incorporation of metal ions (Zn and Ca) and halogens (Cl). These modifications influence the mechanical properties of the fang in a graded manner from tip to base, allowing it to perform as a multi‐use injection needle that can break through insect cuticle, which is made of a chitin composite as well.

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Spiders have highly developed mechanosensory systems, some of which provide access to forms of stimulation alien to our own sensations. Studies of hair-shaped air movement detectors (trichobothria) and tactile sensors have uncovered an outstanding refinement of the processes of stimulus uptake and stimulus transformation, which reflect details of both stimulus physics and behavioral significance. They also emphasize the potential contained in the seemingly simple Bauplan of arthropod cuticular hairs. Embedded into the spider exoskeleton are several thousands of strain detectors (slit sensilla) measuring compressive exoskeletal strains induced by various forms of loads and forces. A compound slit sensillum (lyriform organ) on the leg has become an important model system for studies of mechanoreceptor primary processes at the cellular and membrane level.

Transmission of natural and arteficial vibrations in webs of Nephila clavipes was examined using laser Doppler vibrometry to determine how this spider discriminates and localizes stimuli. 1. Vibration signals of four entrapped insect species peaked at different frequencies from 5--30 Hz, but their spectra overlapped considerably. Peak amplitudes spanned 50dB. 2. Transmission of longitudinal vibrations along individual radii was attenuated over ca. 12cm by 4.0 + 2.7 dB; attenuation values for transverse and lateral vibrations were 22.2 _+ 4.6 dB and 26.2 _+ 4.3 dB, respectively. Some transmission spectra characteristics may be explained by "resonances" of the spider and threads. 3. Radial thread transmission increased by 2.2-5.8 dB after cutting the connecting auxiliary spirals, demonstrating that vibrations "leak" from stimulated radii via these threads. Auxiliary spirals provide structural support to Nephila webs at the expense of degraded directional transmission. 4. Upon single-point stimulation, vibrations measured around the web hub and at the spider's tarsi revealed 2-D vibration amplitude "gradients" of 20-30 dB indicating the stimulus direction. In contrast, measured vibration propagation velocities of 70-1500m/s resulted in time-of-arrival differences at the spiders tarsi of < 1.5 ms, which may be too brief for stimulus direction determination.

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