Spider webs are used like harps, with spiders plucking at the strings to produce different frequencies of movement. Spiders can then feel the frequencies of the resulting movements to learn about prey that may be caught in the web.
Spiders have special sensors in their legs, called slit sensillae, that provide them with perceptions of movement in spider webs. The spiders use these sensors to perceive the different frequencies of vibration in the web strings and this tells them how to navigate in the web to get to their prey. A harp has strings that, when plucked, produce different frequencies of soundwaves that are picked up by sensors in the inner ear and are then perceived as sounds. This is how spider web strings are similar to the strings of the harp.
The Oxford Silk Group at Oxford University, which is led by Professor Fritz Vollrath, studies spider silks mostly as a material that could be used in engineering problems. This group will publish their work on spider silk and a spider’s ability to sense frequencies of web movement in a future edition of the journal Advanced Materials. The report will show how they learned that spider silk can be tuned to a wide range of harmonics.
The Oxford Silk Group has been studying silk because it is exceptionally strong and this ability to produce fine-tuned frequencies may be of use in many engineering situations. When plucked, the strings of the web move only in units of nanometers. The scientists in the Oxford Silk Group used lasers and high-speed cameras to detect these very fine movements. A possible use for these strong silk threads that vibrate at such small frequencies is in communication networks.
All sensory systems, such as vision, hearing, smell, taste and touch, work in a similar way. There is a specific physical stimulus (type of energy) that will stimulate the receptors (specialized cells) for that sensory system. For example, light is the physical stimulus for vision and rods and cones in the retina are the receptors for the visual system; soundwaves are the physical stimuli for hearing and the hair cells in the inner ear are the receptors for the auditory system. Then the cells begin to process the information and send it to the brain. The brain finishes processing the information about the stimuli and perceptions appear. One sees the light or hears the word.
The receptors in the legs of spiders that sense movement, the slit sensillae, work just like other sensory system receptors. The spiders get sonic echoes from the plucked strings in the spider web to get information on prey, potential mates and the structure of the web. The spider webs are used like harps in that the plucked strings of a harp produce soundwaves that create sound perceptions and the plucked spider web strings produce movements that give the spider perceptions of the state of the overall web.
When spider webs are used like harps, spiders are sensing the relative frequencies produced by plucking and the subsequent movements in the spider web. It must sound like glorious music to them to “hear” the web move such that they know they have captured a fly or found a mate.
By Margaret Lutze