The water had then got higher. Not in a single convulsive flood that would have drowned the ants in their burrows, but a little at a time. The ants had edged toward higher ground, which was where people tended to build houses. Houston was the third-largest city in North America. So the result was what Dr. Rutledge dryly called human/ant encounters on a scale never before seen, with thousands of emergency room visits not just from ant bites but collateral damage such as Texans setting fire to themselves when trying to burn ant nests with gasoline.