Spiders, Birds, and Snakes, Oh my!

To continue our spooktacular posts this October, we bring you a study which may have some arachnophobes rethinking their next vacation destination.

The island of Guam is home to one of the densest spider communities in the Pacific.  In a recent study published with PLOS ONE, researchers investigated this region to discover how the demise of insectivorous birds inhabiting the island has affected one of the most widely feared creepy crawlers.

The downfall of Guam’s native insect-eating birds began in the 1940’s when the infamous brown tree snake was introduced.  To investigate the effects this loss had on the landscape, the authors of the recent paper analyzed the spider population on several Pacific islands.

The team compared the neighboring islands of Rota, Tinian and Saipan, to Guam. These islands do not have any known snake populations, and also have similar native bird species to that of Guam.  The researchers were then able to assess whether the bird presence correlated with spider web numbers, in addition to what impact bird presence had per season.

What the authors found might send chills right down your spine: The spider web densities in Guam were 40 times higher than those of the other islands during the wet season. Guam had an average of 18.37 spider webs per 10 meters, as compared to the other islands, which only had 0.45 webs per 10 meters. In addition, the bird loss had even increased the web size for a certain spider species.

Whether you suffer from arachnophobia, ophidiophobia (fear of snakes) or ornithophobia (fear of birds), I think we can all agree this is a terrifying case showing the effects the removal of an essential predator can have to a landscape.

Citation: Rogers H, Hille Ris Lambers J, Miller R, Tewksbury JJ (2012) ‘Natural experiment’ Demonstrates Top-Down Control of Spiders by Birds on a Landscape Level. PLoS ONE 7(9): e43446. doi:10.1371/journal.pone.0043446

Image Credit: Anders B on Flickr CC-by license

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