How do insects like ants time their emergence so precisely?

This week's question comes from Nathan Ehret from Vancouver. He asks:

In my home city, I've noticed that each year on one specific day in early Summer, swarms of flying ants suddenly emerge and fill the air. By the next day, they've basically disappeared. How do such large masses of insects time their emergence so precisely?

Rob Higgins, an associate professor in the Department of Biological Sciences at Thompson Rivers University in Kamloops, says the timing of these events has a lot to do with the weather.

Also, different species of ants reproduce at different times of the year. Carpenter ants are among the first species to emerge in spring. They prefer to under go their mating flights on a calm, sunny day after a substantial rainfall. This makes it easier for the newly mated queens to begin a colony in the the now softer soil and wet wood. Flying ants also prefer a rainfall in order to time their mating in the early summer.

In Vancouver, when there is little rain at that time, they do something different as they did last summer. In early July, Vancouverites reported swarms of flying ants appearing on the same day. Previous to that day, the city reported a heat wave. In this case, the flying ants were able to coordinate their mating flights based on that heat wave. Similar to a rainfall event, these ants were able to time their emergence based on a different type of weather they could all recognize.