How far can spi­ders ‘fly’?

BBC Wildlife Magazine - - Q&A - He­len Smith

The au­tumn spec­ta­cle of gos­samer on the breeze is a re­minder that spi­ders – par­tic­u­larly our small­est species and the spi­der­lings of many larger species – can take flight by so-called ‘bal­loon­ing’.

Most spi­ders travel rel­a­tively short dis­tances, yet some be­come pioneers. Their rapid coloni­sa­tion of iso­lated vol­canic is­lands and Charles Dar­win’s fa­mous ob­ser­va­tion of thou­sands of tiny spi­ders land­ing on the rig­ging of The Bea­gle 100km off the South Amer­i­can coast at­test to their long-dis­tance ca­pa­bil­i­ties. Al­ti­tudes, too, are im­pres­sive, with in­di­vid­u­als recorded in the aerial plank­ton sev­eral thou­sand me­tres above the Earth.

Bal­loon­ing is an en­er­get­i­cally cheap form of trans­port but, what­ever the dis­tance trav­elled, just go­ing with the wind comes at a cost. Only a few aero­nauts will sur­vive their risky jour­neys – a price worth pay­ing only when the chances of colonis­ing pas­tures new out­weigh the risks of over­crowd­ing at home.

To bal­loon, spi­ders stand on tip­toe, raise their rear ends and dis­pense a puff of silk from their spin­nerets, which car­ries them on the breeze.

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