Even the elders in Pakistan's Sindh province admit they've never seen anything like it: whole trees encased in webs by millions of invading spiders. The mysterious phenomenon may be an unexpected result of the devastating floods that swept over Sindh, reports Wired. According to scientists, the spiders likely collected in the trees after fleeing from the rising floodwaters. At their height, the floods covered as much as a fifth of the country and displaced as many as 20 million people. One unexpected blessing from the bizarre post-flood event is that the hungry spiders seem to be significantly reducing mosquito populations. Malaria and other mosquito-borne diseases became a serious concern in the region after the floods receded and left the landscape blanketed in stagnant water. But areas of Sindh with the most web-covered trees also have reported fewer cases of malaria. It's a strange fix for such a pervasive problem, but nature has an odd way of striking a balance. Since reconstruction in the worst-hit regions of the country could take years, the cocooned trees may turn into an unexpected symbol of nature's good will — in spite of their spookiness. More photos, courtesy of the U.K.'s Department for International Development, reveal the alien-like world of the webbed trees: