Boxing gloves were nowhere in sight for a world spider heavy-weight title challenge at the Natural History Museum last month. The contenders were the Hercules baboon spider, and the current Guinness World Records (GWR) holder for world’s heaviest spider, the Goliath bird-eater.
Museum bug expert George Beccaloni was contacted by GWR life sciences consultant Karl Shuker after reports of a possible rival. Karl asked George if he could check the size of the Hercules baboon spider as the Natural History Museum has the world’s only known specimen and George is the author of the Museum book, Big Bugs Life-Size. Using a jar of alcohol and the Archimedes' Principle, both specimens were submerged to discover the volume of alcohol they displaced, and therefore the volume of their bodies.
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Spider specimens are stored in alcohol and this makes their internal organs shrink. The water inside them gets replaced by alcohol, which is about 25% lighter than water. This means that their weight when they were alive would be about 25% greater. Knowing that they would weigh about 1g per cubic cm when alive means that their weights can easily be calculated if their body volumes are known.
The female Goliath bird-eating spider specimen measured 69 cubic cm, more than double the volume and therefore the weight of the Hercules baboon spider that measured 22 cubic cm. So the Goliath bird-eating spider remains the world's heaviest spider species, with the heaviest recorded individual being a 12-year-old captive female called Rosi - according to GWR, it had a body length of 119.4mm and weighed a massive 175g.
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