If they went to the water fountain instead of the hummingbird feeder I'd say they don't need the sugar syrup now. They do need water and lots of it right now until it cools down again. They use water to cool the hive through evaporation. They try to keep the hive temperature around 93ºF so when it's really hot outside the hive you can imagine how hot it is inside. DH gave ours extra ventilation by propping the outside cover a little bit to let the heat escape out the top. They still require extra water but the extra ventilation helps them out some.
