Roundworms are intestinal parasites that are prevalent in rural and impoverished areas worldwide, including the southern United States. Infections by such parasites may result in anemia, malnutrition and death. Current efforts to control roundworms use antihelminthic drugs to remove the adult worm after it infects its human host. However such control measures are costly, difficult to administer in developing nations and may be losing their effectiveness. We propose a novel approach to controlling these parasites by targeting a life history trait that is common amongst several prevalent parasitic worms; a free-living juvenile stage where the larvae of the worm thrives in soil and eats bacteria. Using the tools of synthetic biology, we propose to engineer bacteria that are genetically modified to produce toxins that kill roundworm larvae upon ingestion. To accomplish this, we will engineer the bacterium Escherichia coli to be preferentially consumed by, and produce toxins to kill, the model roundworm Caenorhabditis elegans as well as additional species of non-parasitic hookworms. If successful, our approach would represent a major advance in the attempt to control parasites that infect over 740 million people worldwide and will represent a significant advancement in the field of synthetic biology.