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.