Smithsonian.com

Darwin's bark spider spins the world's longest webs. Credit: M. Kuntner

As a young girl, I used to wake up in the middle of the night, frightened by a spider I knew had to be lurking in some dark corner of my room. For arachnophobes such as myself, nothing could be more unsavory than a big spider that blends seamlessly into tree bark. Unless that same spider also spins the largest, strongest webs in the world.

A new species of bark spider in Madagascar—called Darwin’s bark spider (Caerostris Darwini) and discovered in 2009, the 150th anniversary of the publication of On the Origin of Species—has evolved the toughest silk scientists have ever seen, and the spiders use it to spin the biggest webs ever measured. According to the study (pdf), these spiders, whose bodies are up to 1.5 inches in diameter, spin orb-shaped webs suspended on “bridgelines” that can span more than 80 feet. The spiders build webs over lakes, rivers and streams. Several different insects were found wrapped in the spiders’ silk, including mayflies, bees, dragonflies and damselflies.

Scientists from the Smithsonian’s National Museum of Natural History, as well as universities in Slovenia and Puerto Rico, found these spiders to be the first to ever spin webs over bodies of water this far above sizeable rivers. They believe such a tough feat is possible only because of their incredibly tough silk.

This is one more thing to add to the long list of extraordinary bark spider characteristics. The eleven known species of bark spider (genus Caerostris) look strikingly like tree bark, and are difficult to see. Females, the only ones who spin these gigantic webs, are several times bigger than male spiders and tend to be much more visible than their male counterparts. Scientists believe that the diversity of Caerostris spiders is grossly underestimated. And because males and females look so drastically different, it can be nearly impossible to determine which bark spiders are of the same species. These critters also have notoriously strange mating behaviors, involving male aggression, mate guarding, and some other practices we won’t go into here.

Don’t get me wrong—Madagascar always sounded like a spectacular destination. But if I do go, I’ll be sure to stay away from the water so I don’t get caught in these super strong, gigantic webs.

(Check out Smithsonian Science for a video of a Darwin’s bark spider subduing a dragonfly on her web.)