Spiders, unlike humans and many other animals, lack eardrums to perceive sound. This can lead to the misconception that these creatures are deaf. However, spiders navigate their environment and interact with it through an intricate sensory system that primarily relies on detecting vibrations, which serve as their equivalent of “hearing.”
How Spiders Detect Vibrations
Spiders rely on specialized mechanoreceptors to detect vibrations. Two types are trichobothria and slit sensilla. These organs are distributed across their bodies, especially on their legs, allowing them to pick up minute environmental movements.
Trichobothria are highly sensitive, elongated hairs protruding from a spider’s exoskeleton, especially on its legs and pedipalps. These fine hairs are suspended in a flexible membrane, allowing them to respond to the slightest air movements, including sound waves. When deflected, they stimulate nerve cells, transmitting signals about the presence and direction of airborne vibrations. They are so sensitive they can detect air movements at an atomic scale.
Slit sensilla are microscopic, slit-like openings in the spider’s exoskeleton, often found in clusters called lyriform organs, especially near leg joints. These sensilla detect mechanical strains and vibrations in the spider’s cuticle. When the exoskeleton deforms due to vibrations, sensory neurons beneath these slits are stimulated, informing the spider about substrate-borne vibrations. Orb-weaving spiders, for instance, use their webs as an extended sensory organ, detecting vibrations traveling through silk strands.
The Spectrum of Spider “Sound” Perception
Spiders utilize their ability to detect vibrations for various behaviors, including hunting, predator avoidance, and communication. The type and frequency of vibrations help them distinguish between different stimuli sources. This vibrational information aids their survival and reproduction.
For hunting, spiders use vibrations to locate prey. Jumping spiders, for example, detect airborne sounds from several meters away, including low-frequency insect wingbeats, to pinpoint meals. Orb-weaving spiders interpret vibrations through their webs to identify caught prey, distinguishing insect movements from disturbances like wind or debris. They can even triangulate the exact location of a vibration source on the web by processing slight time differences in how vibrations reach their legs.
Vibrational cues also play a role in avoiding predators. Some jumping spiders are sensitive to low frequencies, such as 80-130 Hz, matching predatory wasp wingbeats. Upon detecting such sounds, they may exhibit freezing behavior. This allows them to react to threats even when they cannot visually perceive them.
Spiders communicate through vibrations, particularly during courtship and mating. Male spiders often produce specific substrate-borne vibrations by drumming their pedipalps or abdomens on surfaces, or by plucking and shaking a female’s web silk. These vibrational patterns convey information about the male’s species, size, and quality to a potential mate. Male courtship vibrations can even delay predatory behavior in females, reducing the risk of being mistaken for prey.