When a series of devastating floods in 2010 brought huge swaths of Pakistan to its knees, the spiders were forced to move into the trees to survive. As a result, the webs they constructed have smothered the trees and are slowly killing them. In a bizarre twist, however, the webbed trees are trapping and killing such a vast percentage of the mosquito population that malaria cases are plummeting thereby saving many lives. Nature works in the most mysterious ways sometimes.
Source: New Scientist