Have spiders ears
Can spiders hear? Or: do spiders have ears?
In humans, the ear captures sound waves. Sound waves are nothing more than moving or vibrating air. These vibrations are passed on in the inner ear via a filigree system. The brain then processes the whole thing into a sensory impression that we call hearing.
Spiders can hear even without ears, provided that this is understood to mean that they perceive air vibrations and currents and process these stimuli. How does that happen?
Cup hairs, trichobothria
Spiders are known to have hairy legs. For the spider, the hairiness is of paramount importance for the perception of the outside world. The hair on the legs differs structurally from each other and, depending on the structure, perform different functions. For example, a distinction is made between whisker hair and cup hair on the legs. When asked about the ability of the spiders to hear, the goblet hairs are of particular interest. When the function of the cup hairs was first described, they were also called auditory hairs (1). The term trichobothria (2) or cup hairs later became established. It is long, very fine and very flexible hair that is turned into a "cup" in the exoskeleton of the legs. Even the slightest movement of air is enough to make it vibrate. Due to their sensitive properties - they are directly connected to nerve cells - a perceptible stimulus arises for the spider, which the spider can also classify and process.
In nocturnal spiders in particular, this stimulus processing plays a key role in locating the prey (3). Imagine the following: an insect flies towards a spider. The movement of the wings creates extremely fine air vortices. The highly sensitive trichobothria are moved by the air flow and this movement enables the spider to locate the approaching insect so precisely that it can successfully attack it.
Hear from three meters away
While it was long thought that spiders only react to air vibrations in their immediate environment, it was not long ago discovered that spiders can also perceive sounds several meters away.
Researchers at Cornell University, Ithaca, New York (USA) were able to prove this in a jumping spider (4). Chance sometimes helps with such discoveries. The Washington Post reports how the researchers made their discovery (5). Another experiment was to measure neural activity in a jumping spider. When a chair was moved a few meters away, the measuring device gave a feedback. As a result, curious, the researchers were able to demonstrate with further experiments that the animals can actually perceive certain noises in the low frequency range from a distance of up to 3 meters. They also found that the spider froze at these noises, "A [...] behavior that is characteristic of an acoustic startle reaction" (6). They concluded that this rigid posture served to make oneself invisible to a predator who was after the spider.
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