Tuesday, January 31, 2012

Spider Brain

Filmy Dome Spider - MDC
Ever wonder how a tiny spider's brain can perform the same tasks as a much larger spider species?  Our common Filmy Dome Spider for instance creates a complex snare web which looks like an upside-down silk bowl.

Part of their secret may be where to keep a big brain too big to fit in their heads.  Eurekalert.org describes research by the Smithsonian Tropical Research Institute in Panama which found that the smaller the spider the bigger their brain is in proportion to their body.  When the brain is too big for the head it is stored in body cavities.  In the smallest spiders, the brain filled 80% of the body cavity with 25% of it in their legs.

There is only so much miniaturization that neural tissue can stand.  Neurons and axons cannot be shrunk and still carry the signal.  Therefore, the spider has to devote more body space to their nervous system.

The study was done in Panama and Costa Rica where a tremendous diversity of spiders allowed for a broad range of comparisons.  The giant spider Nephilia  clavipes weighs 400,000 times as much as the smallest spider in their study.

There is Haller's rule which states that as body size decreases, the proportional mass of the brain goes up.  In a human the brain is only 2-3% of our body mass compared to 15% in ants and even a greater proportion in spiders.  Now if I could just figure out how to use more of it.

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