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Tiny Spiders’ Brains Bulge Out Into Their Legs

Tiny Spiders’ Brains Bulge Out Into Their Legs


Giving a whole new meaning to the phrase “thinking on your feet” Smithsonian researchers have found that tiny spiders have such large brains they fill their body cavity and overflow into their legs.

Researchers measured the central nervous systems of nine species of spiders, from rainforest giants to spiders smaller than a pin head. They found that as the spiders get smaller their brains get proportionally bigger and so fill up more and more of their bodies.

From the Smithsonian Tropical Research Institute press release:

“The smaller the animal, the more it has to invest in its brain, which means even very tiny spiders are able to weave a web and perform other fairly complex behaviors,” said William Wcislo, staff scientist at the Smithsonian Tropical Research Institute in Panama. “We discovered that the central nervous systems of the smallest spiders fill up almost 80 percent of their total body cavity, including about 25 percent of their legs.”


“We suspected that the spiderlings might be mostly brain because there is a general rule for all animals, called Haller’s rule, that says that as body size goes down, the proportion of the body taken up by the brain increases,” said Wcislo. “Human brains only represent about 2-3 percent of our body mass. Some of the tiniest ant brains that we’ve measured represent about 15 percent of their biomass, and some of these spiders are much smaller.”

The huge level of biodiversity in Panama and Costa Rica made it possible for researchers to examine spiders with a wide ranging difference in body sizes.

This discovery was made as part of ongoing research to understand the link between a creature’s size and its brain size and behavior.


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Image used under the Creative Commons Attribution License with thanks to derekkeats.

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7:32AM PST on Dec 16, 2011

Goodness Jane B.
Why the negative comments? People study whatever they please, and if spiders are what interest them, then let them study spiders. If I used tax money to study horses would you be equally offended?
I thought this information was very interesting!

5:08AM PST on Dec 16, 2011

We need to elect some really tiny Congress members.

4:07PM PST on Dec 15, 2011


3:09PM PST on Dec 15, 2011

Whoever thought up this study lost his thinking mind. I hope I didn't pay for it. The information gained from this is only of value to another spider. Is this lab informing the spiders?

2:39PM PST on Dec 15, 2011

:/ ugh, I know spiders are useful but I hate them anywhere near me

1:52PM PST on Dec 15, 2011

Ha! Really interesting.

11:47AM PST on Dec 15, 2011

rene d.

We males actually have two brains,,,one for thinking lofty thoughts and the other for thinking down and dirty. Which one rules depends on the environment,,,

11:30AM PST on Dec 15, 2011

gee small spiders are like some men. spiders keep their brains in their legs and some men keep their brains between their legs.... ha ha

10:18AM PST on Dec 15, 2011

interesting.. and I think spiders are amazing. But my phobia prevents me from being able to be overly appreciative of them. Just the pic gave me chills. yikes

8:44AM PST on Dec 15, 2011

All creatures are amazing and wonderful, and this is a very interesting discovery. I have a deep an abiding respect for all forms of life (mosquitoes and parasites, not so much) and recognize the majority are more intelligent (as humans define intelligence) than most people believe.

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