A whole new meaning for thinking on your feet

Dec 12, 2011
Nephila clavipes, a big tropical spider, has plenty of room in its body for its brain. Credit: Pamela Belding, STRI

Smithsonian researchers report that the brains of tiny spiders are so large that they fill their body cavities and overflow into their legs. As part of ongoing research to understand how miniaturization affects brain size and behavior, researchers measured the central nervous systems of nine species of spiders, from rainforest giants to spiders smaller than the head of a pin. As the spiders get smaller, their brains get proportionally bigger, filling up more and more of their body cavities.

"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."

Some of the tiniest, immature spiderlings even have deformed, bulging bodies. The bulge contains excess brain. Adults of the same species do not bulge. Brain cells can only be so small because most cells have a nucleus that contains all of the spider's genes, and that takes up space. The diameter of the or axons also cannot be made smaller because if they are too thin, the flow of ions that carry is disrupted, and the signals are not transferred properly. One option is to devote more space to the nervous system.

The brains of smaller spiders, like nymphs in the genus Mysmena, extend out of their body cavity into their legs. Credit: Wcislo lab.

"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. " 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."

use a lot of energy, so these small spiders also probably convert much of the food they consume into brain power.

The enormous biodiversity of spiders in Panama and Costa Rica made it possible for researchers to measure brain extension in spiders with a huge range of body sizes. Nephila clavipes, a rainforest giant weighs 400,000 times more than the smallest spiders in the study, nymphs of spiders in the genus Mysmena.

Explore further: Male monkey filmed caring for dying mate (w/ Video)

More information: Quesada, Rosanette, Triana, Emilia, Vargas, Gloria, Douglass, John K., Seid, Marc A., Niven, Jeremy E., Eberhard, William G., Wcislo, William T. 2011. "The allometry of CNS size and consequences of miniaturization in orb-weaving and cleptoparasitic spiders." Arthropod Structure and Development 521-529, doi10.1016/j.asd.2011.07.002

Provided by Smithsonian Tropical Research Institute

4.9 /5 (9 votes)

Related Stories

Why are male spiders small while females are giant?

Aug 02, 2010

'Bridging', an unusual mode of getting around frequently used by vegetation-inhabiting spiders to cross large gaps, may partly explain the tendency for male spiders to be much smaller than females. Researchers ...

Male black widows look for well-fed mates

Jul 07, 2011

(PhysOrg.com) -- According to a new study published in Animal Behaviour, a male black widow spider is able to identify a female spider that has eaten well by simply taking a few steps on the web she spins. ...

Recommended for you

Male monkey filmed caring for dying mate (w/ Video)

Apr 18, 2014

(Phys.org) —The incident was captured by Dr Bruna Bezerra and colleagues in the Atlantic Forest in the Northeast of Brazil.  Dr Bezerra is a Research Associate at the University of Bristol and a Professor ...

Orchid named after UC Riverside researcher

Apr 17, 2014

One day about eight years ago, Katia Silvera, a postdoctoral scholar at the University of California, Riverside, and her father were on a field trip in a mountainous area in central Panama when they stumbled ...

In sex-reversed cave insects, females have the penises

Apr 17, 2014

Researchers reporting in the Cell Press journal Current Biology on April 17 have discovered little-known cave insects with rather novel sex lives. The Brazilian insects, which represent four distinct but re ...

Fear of the cuckoo mafia

Apr 17, 2014

If a restaurant owner fails to pay the protection money demanded of him, he can expect his premises to be trashed. Warnings like these are seldom required, however, as fear of the consequences is enough to ...

User comments : 3

Adjust slider to filter visible comments by rank

Display comments: newest first

axemaster
not rated yet Dec 12, 2011
So... do they have proper stomaches? What about organs?
Squirrel
5 / 5 (1) Dec 12, 2011
It is interesting to note that the current issue of this journal has a paper showing that very small insects such as in the parasitic wasp genus Megaphragmahave (less than 1/5 of a millimeter in body length) have evolved a different solution: neurons without nuclei.
Deesky
5 / 5 (1) Dec 12, 2011
researchers report that the brains of tiny spiders are so large that they fill their body cavities and overflow into their legs

That's the coolest thing I've learned in weeks!

More news stories

Biologists help solve fungi mysteries

(Phys.org) —A new genetic analysis revealing the previously unknown biodiversity and distribution of thousands of fungi in North America might also reveal a previously underappreciated contributor to climate ...

Researchers successfully clone adult human stem cells

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

NASA's space station Robonaut finally getting legs

Robonaut, the first out-of-this-world humanoid, is finally getting its space legs. For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot—now stuck ...

Ex-Apple chief plans mobile phone for India

Former Apple chief executive John Sculley, whose marketing skills helped bring the personal computer to desktops worldwide, says he plans to launch a mobile phone in India to exploit its still largely untapped ...

Filipino tests negative for Middle East virus

A Filipino nurse who tested positive for the Middle East virus has been found free of infection in a subsequent examination after he returned home, Philippine health officials said Saturday.

Egypt archaeologists find ancient writer's tomb

Egypt's minister of antiquities says a team of Spanish archaeologists has discovered two tombs in the southern part of the country, one of them belonging to a writer and containing a trove of artifacts including reed pens ...

Airbnb rental site raises $450 mn

Online lodging listings website Airbnb inked a $450 million funding deal with investors led by TPG, a source close to the matter said Friday.