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Why Are Spiders Spinning Webs On Chicago's Tallest Buildings?

 Spiders routinely occupy window space in Chicago's high-rises.
High-rise spiders
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CHICAGO — As millions of birds are flying their way through Chicago, even more spiders are making a trek up the city's tallest buildings.

Like the birds that are migrating north through the city during the spring, countless spiders climb up to the highest reaches of Chicago's skyline, inhabiting window space with their webs and dining on various high-flying bugs.

"On most high-rise windows you should be able to find one," said Allen Lawrance, the Invertebrate Specialist at Peggy Notebaert Nature Museum. "They are everywhere. I find them really interesting."

Some baby spiders even spin webs in the shape of balloons that are captured by the wind and carried all over Chicago, including the tops of Willis Tower, Hancock Center and other high-rises.

Most of the spiders are Larinioides Sclopetarius, known as the bridge spider or gray cross spider. The spiders usually live on rocks overhanging water, which is similar to a high-rise. The spiders also are attracted to the lights coming from the high-rises.

The high-rise spiders are dining on flies, moths, butterflies and other insects. Lawrance said insects have been found flying at nearly 20,000 feet, and there's plenty of food to be eaten by skyscraper spiders. If insects aren't available, high-rise spiders are known to be cannibals, said Lawrance, a University of Illinois graduate and Lakeview resident.

In past years, Downtown hotels have warned guests to keep their room windows closed a preventative measure against spiders finding their way inside.

Lawrance said high-rise spiders won't bother you as long as you keep your windows closed. If you want less spiders around, try turning your lights off during nighttime hours, he said.

"A porch light will attract them," he said.

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