The life cycle of a mosquito from egg to adult can be completed in less than a week, depending on water temperature and the species of mosquito. Eggs deposited on water surfaces usually hatch within a day or so, while those deposited in soil can hatch months or even years later depending on water availability. On average, the female usually deposits from 100 to 150 eggs at a time. Over the life course, the female mosquito may deposit three to four batches of eggs.
That's why it's important to dump and drain all standing water where mosquitoes lay their eggs.