Hookworms have a complex life cycle that begins and ends in the small intestine. Using the CDC chart (please see attached PDF file below), adult female worms produce thousands of eggs (adults can produce 15,000 to 20,000 eggs a day which exit in the feces), which are excreted in stool (#1 below). Hookworm eggs are not themselves infective. However, if they reach soil (for example, when infected persons defecate on the ground or when "night soil" is used to fertilize crops) and if the soil conditions are favorable (warm, moist, and shaded), the eggs hatch into larvae (#2 below). Within seconds, the barely visible larvae penetrate the skin (#3 below), usually through bare feet (#4 below) where an itchy rash called ‘ground itch’ sometimes develops. Often, people do not feel the initial penetration. The larvae enter the airways by migrating to the lungs by way of the bloodstream. They then travel up the windpipe and cause coughing, where they are then swallowed. When the larvae are swallowed, they eventually reach the small intestine and then attach to the intestinal wall by hooks (see picture below). There they develop into adult worms (which can take 6-7 weeks), and infect the small intestine (#5). This journey takes about a week. In the small intestine, the larvae develop into half-inch-long worms (7-13mm), attach themselves to the intestinal wall, and suck blood and nutrients.