In Borneo in the 1950s,mosquitoes were giving people a disease called malaria. When people are ill with malaria,they feel hot,then cold,and very tired; sometimes they ever die. So the government used a lot of pesticide called DDT to kill the mosquitoes. Soon there was less malaria-and that was a good thing. But then the grass roofs of people's houses started to fall on their heads. Why? Because, wasps ate the caterpillars, but the DDT was killing the wasps, too. Now there was nothing to stop the caterpillars, and so the roofs started to fall down. Then there was a bigger problem.