Most spiders are silent to the human ear because they lack vocal cords and cannot produce sounds like mammals. However, a select number of species, particularly larger arachnids like tarantulas and certain jumping spiders, have evolved specialized structures to produce audible sounds or vibrations. These acoustic signals are a form of communication, serving a direct purpose in the spider’s interaction with its environment or other members of its species.
The Auditory Reality of Spiders
The reason humans seldom hear spiders relates to the physics of their communication, which is predominantly through vibration rather than airborne sound. Most spider communication occurs through substrate-borne signals, meaning the sound travels through the surface the spider is standing on, such as a leaf, the ground, or a web. These vibrations are not efficiently transmitted into the air as sound waves, requiring scientists to use sensitive equipment, like laser vibrometers, to record and analyze the faint signals. The most notable exceptions are larger spiders, such as tarantulas, whose sound production is powerful enough to be heard several feet away. These species produce a hissing or buzzing noise loud enough to cross the threshold of human hearing.
Mechanisms of Sound Production
Spiders generate sounds through two primary physical processes involving moving specialized body parts against another surface. The first method is stridulation, which involves rubbing two different body parts together to create friction, similar to how a cricket chirps. In spiders, this apparatus can be located on the legs, the abdomen, or the pedipalps (small, leg-like appendages near the mouth). For example, a tarantula may rub bristles on its abdomen against its carapace, producing a distinct hissing or buzzing sound.
The second major method is drumming or tapping, which involves the spider rapidly vibrating or striking a surface with its legs or pedipalps. This action transmits a seismic signal directly into the substrate, allowing the vibration to travel across the ground or the web.
Male wolf spiders use rapid, rhythmic tapping motions during courtship, sending species-specific vibrational patterns into the earth or leaf litter. Jumping spiders also engage in this substrate-borne signaling, often using complex, rhythmic footwork.
Why Spiders Vocalize
The sounds and vibrations spiders produce are primarily used for communication related to reproduction or self-preservation. One main reason for acoustic signaling is courtship, where males use vibrations to announce their presence to potential mates. For web-building spiders, the male’s courtship vibrations must be distinct from the signals made by trapped prey to prevent the female from attacking him. Male jumping spiders also use complex vibratory signals that convey information about their size and genetic quality to a female. On the defensive side, the loud hissing produced by some tarantulas, such as the Australian barking spider, is a clear warning signal meant to startle and deter a potential predator.