Species: Caerostris darwini
Habitat: Madagascar, alarming arachnophobes and mayflies in equal measure
The spider attaches a line of silk to the tree branch she is standing on, by the side of a river, and bungee-jumps into space. Dangling in mid-air, she begins spewing out silk. And more silk. And still more silk.
Eventually she has released more than 25 metres of continuous strands, which drift away downwind, across the river. Suddenly she stops, and begins reeling the line back in. It pulls taut. Success! The other end has tangled itself in a bush on the far bank.
This is the first step in the construction of the world’s biggest spider web, which will hang above a tropical river. Perched in the centre of her vast web, the Darwin’s bark spider can feast on huge numbers of insects after they emerge from the water.
The Darwin’s bark spider was discovered in Madagascar only last year, by Matjaž Kuntner of the Slovenian Academy of Sciences and Arts in Ljubljana and Ingi Agnarsson of the University of Puerto Rico in San Juan. With Kuntner’s colleague Matjaž Gregorič and Todd Blackledge of the University of Akron in Ohio, they have carried out more field studies to find out how the spiders build their webs and what they are for.
The Darwin’s bark has a built-in advantage. Its silk is the toughest of any spider, which is particularly remarkable as spider silks are tough anyway, and stronger than many artificial substances.
The river-spanning lines of silk are the longest section of the web. The spider’s method of building them – trailing silk into the open air and hoping for the best – is similar to the common spider trick of “ballooning”. Spiders who want to travel long distances release long strands of silk that act like kites and pull the spiders into the air. Ballooning is found in most species of spider, suggesting it has an ancient evolutionary origin – the bridging lines may have developed from it.