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jeudi 7 août 2014

Animals that don't Exist

The Singing Spider

The singing spider, Misumena cantante, is a rather peculiar species of crab spider found throughout Spain, Italy and the south of France. Like most crab spiders, it is an ambush predator, waiting for its prey to stray within its reach. Except that when the prey does, the singing spider does not pounce. It starts to sing.
Singing spiders emit a high-pitched sound, which immobilizes their prey. Depending on the prey, they modulate the sound in four to five different patterns, which vary with the region they inhabit. While continuing to “sing”, the singing spider “dances” around its prey to tie it up with its silk. Once they prey is securely tied up, it then proceeds to inject its venom.
The hunting method of the singing spider might be long-winded in comparison with that of other crab spiders (the singing spider's “performance” can last up to thirty minutes, whereas other species of the same family only need a couple of seconds to kill their prey), but it allows them to catch much bigger prey than they could otherwise. A fully-grown female singing spider measures around 1 cm (0.39 inches), and is capable of capturing invertebrates of up to 5 cm (2 inches). Although the males are distinctively smaller than the females, they too can catch prey of up to 5 times their body size.
Morphological studies at the “Institut de Recherche de la Musicalité Insectoïde” (IRMI), in Toulouse, have shown that a series of openings in the underside of the thorax, which can be closed and opened, and that are connected to the trachea in the abdomen, and through which they can pump air through muscular contraction, are used to produce the paralyzing sound. In other spiders, no muscular contraction is used for breathing, which is why doctor Louis de la Raignée, the lead scientist for the IRMI study, believes that this mechanism has evolved solely for the purpose of “singing”.
It has been observed that it will only “sing” to prey that is at least three times its size. Otherwise, it either hides in a hole it digs in the ground, or, if the prey is small enough, catches it with its chelicerae. This is probably due to the high risk of detection by predators during capture. The size of the prey is directly related to the trade-off between risk and benefits, and it has been shown that depending on perceived risk of predation, minimum “singing” size will change in a predictable manner. Since maximum size does not change, it is believed that the increase in effort for capture of prey increases less than the payoff. Thus, the upper maximum must be related to the tensile strength of the silk.
Curiously, the different patterns of singing spiders are closely related to the “traditional” music of the regions in which they live. It has been observed that singing spiders in captivity will modify their patterns depending on the music they listen to (which can greatly influence their hunting success rate). Although this seems to indicate that the spiders are the ones adapting to their environment, genetic studies by the IRMI show that the dispersion of the singing spider, originating in Italy, precedes the spread of Italian music during the Renaissance by an estimated ten to twenty years.

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