On the Kenya coast Aedes aegypti breeds in pots maintained indoors for water storage. Pupal numbers vary greatly from one pot to another. The rhythm of water replenishment and the accidental introduction of food into the pots regulate pupal numbers. When water replenishment occurs more often than once per week, pupal numbers are small. When replenishment occurs less often, both low and high pupal numbers may be observed. The presence or absence of larval food distinguishes pots of high versus low productivity. A hypothesis is put forward that the introduction of food into the pots could be the result of human activity especially of young children when getting water for their meals.