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 Editor-in-Chief Craig Glenday after reports of a possible rival. Craig 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.
Craig was there to adjudicate when George measured the two spiders. 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.
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.
'Rosi was considerably heavier than the Museum specimen that we measured,' says George. 'It's amazing to think that she weighed about as much as 5.8 house sparrows!'
'People who have seen the Hercules baboon specimen, without a specimen of the Goliath bird-eater beside it, have been impressed by how huge it is and this has led to the myth that it might be the world's largest spider.'
Hercules baboon spider
The Hercules baboon spider, Hysterocrates hercules, specimen was collected over 100 years ago in Nigeria. Virtually nothing is known about this species but, in common with other baboon spiders, it probably lives in a burrow in the ground and comes out at night to hunt its prey.
Goliath bird-eating spider
The 2cm-long fangs of the Goliath bird-eating spider, probably the longest of any spider.
The 2cm-long fangs of the Goliath bird-eating spider, probably the longest of any spider. © George Beccaloni
A lot more is known about the world champion, however as it is commonly kept as an exotic pet. The Goliath bird-eating spider, Theraphosa blondi, is found in north-eastern South America, preferring wet mountain rainforest. It’s a nocturnal creature spending most of its time in a silk-lined burrow.