The hookworm thrives in warm soil where temperatures are over 18 °C. They exist primarily in sandy or loamy soil and cannot live in clay or muck. Rainfall averages must be more than 1000 mm (40 inches) a year for them to survive. Only if these conditions exist can the eggs hatch. Infective larvae of "N. americanus" can survive at higher temperatures, whereas those of "A. duodenale" are better adapted to cooler climates. Generally, they live for only a few weeks at most under natural conditions, and die almost immediately on exposure to direct sunlight or desiccation.