Spider Infested Building

(Source: Daily Mail)

Although this is not technically a modern ruin--the building was the Baltimore Waste Water Treatment Plant--it sure looks like it. According to the Daily Mail report, the web was discovered in 2009, covered approximately 4 acres, and was home to an estimated 107 million spiders. (More from Wired Magazine). The weight of the webs was so great that it was pulling light fixtures out of the ceiling. 

On a related note, a massive spider web covering several acres of oak-elm woodlands along a Lake Tawakoni State Park trail was discovered in early August 2007. (More from the New York Times).

(Source: Science Daily)