Real Girls: What creature has 32 brains?


	October 23, 2024

Original photo by Vtmila/ Shutterstock

Leeches have 32 brains.

Humans love to think we're the brainiest species around, but leeches have an impressive 32 brains (making them absolute shoo-ins if Mensa ever expands their ranks to include nonhuman animals). These bloodsucking invertebrates are biologically divided into around 32 separate sections, each of which features its own brain fragment. In addition to housing a leech's thought centers, these segments serve additional functions: The first few contain a leech's eyes and front sucker, the middle sections are where you can find the bulk of a leech's nerves and reproductive system, and the rear portion is home to yet another sucker at its tail end.

Yet leeches are far from the only living things with more organs than you might expect. Cuttlefish, squid, and octopuses all have three hearts — a systemic heart to pump blood throughout the body, and two branchial hearts used for pumping blood through the gills. Cows famously have a stomach with four separate compartments, but that's nothing compared to the Baird's beaked whale, which can have as many as 13 stomachs. Perhaps no animal is more unusual, however, than the Ramisyllis multicaudata, a sea worm with hundreds of butts, each with its own set of eyes and brain.

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		Numbers Don't Lie

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Leeches were once used to predict the weather.

In 1851, an English doctor by the name of George Merryweather attempted to repurpose medicinal leeches for weather forecasting. Merryweather noted that leeches would rise in water as rain neared, perhaps reacting to the change in air pressure, and decided to use that phenomenon to create his Tempest Prognosticator. The machine was essentially a leech barometer, and featured a circle of glass bottles, each containing a leech in rainwater. As atmospheric conditions changed, the leeches would crawl to the top of the bottles, dislodging a pin that would ring a bell. Merryweather hypothesized that the more bells that rang, the more likely it was that a storm was approaching. The Tempest Prognosticator debuted at the Great Exhibition of 1851 and was later recreated for the Festival of Britain in 1951, although it failed to achieve any sort of widespread success, due to the dubious science behind the concept.

Today's edition of Interesting Facts was written by Bennett Kleinman and edited by Bess Lovejoy.