Sugar water for hummingbirds should be changed every 1-2 days, especially during hot weather, to prevent spoilage and the growth of harmful bacteria. The nectar can ferment quickly and spoil, becoming toxic to the hummingbirds. A feeder that has not been cleaned regularly can also attract bees and wasps, which can be a threat to the hummingbirds. To keep your hummingbirds safe and healthy, make sure to change the nectar frequently and clean the feeder thoroughly between fillings. If the weather is hot, you may need to change the nectar more often.