Small Spiders’ Brains Fill Up Most of Their Body Cavity

If spiders weren’t creepy enough… It turns out that the smaller a spider is, the larger its brain is in proportion to its body size. This is how a tiny spider and a huge spider can have equally complex behaviour. What this means anatomically is that in some spiders, the central nervous system takes up as much as 80% of the body cavity, with their brains literally spilling into their legs. 

More from National Geographic:

Taking up so much body space for a brain would seem to be a problem for a spider’s other organs, Eberhard said. “But [that aspect] hasn’t really been studied.”

Just by the way the spiders look, though, it would make sense that the arachnids are trading something for their big brains.

For instance, in the jumping spider Phidippus clarus, which the researchers examined in a separate study, the adult’s digestive system is in the spider’s cephalothorax—its head and body cavity.

But “in the young one, all that stuff is filled up with brain,” and the baby spider has a less developed digestive system. It’s still unclear, though, what impact this has on the developing spiders…

Presumably, large brains are necessary to spin webs, a behavior thought to be more complex that, say, “a larval beetle that simply eats its way through the fungus where it lives,” Eberhard wrote in an article describing the research…

It’s a weird concept, having so much of a body filled up with the central nervous system (brain and spinal cord). I wonder how or if it relates to spiders’ reaction times, if their sensory organs (including skin) are so very close to their central nervous system. Is there a difference in reflexes between small and large spiders, or young and adult, attributable to relative brain size? Maybe we’ll find out in the future!


One Response to Small Spiders’ Brains Fill Up Most of Their Body Cavity

  1. Pingback: Watching Me

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