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11 animals that have a sixth sense

By: Bryan Nelson on Sept. 22, 2010, 1:20 p.m.
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All spiders have unique mechanoreceptory organs called slit sensilla, which allow them to sense minute mechanical strains on their exoskeleton. This sixth sense makes it easy for spiders to judge things like the size, weight, and possibly even the type of creature that gets caught in their webs.

It may also help them tell the difference between the movement of an insect and the movement of the wind, or even a benign blade of grass, as it moves across the web.