What is a nuptial flight?

Once a year a mature ant colony makes a batch of winged ants and sends them all up at once to mate. That flight is the entire point of the colony's year. The foraging, the nest-building, the millions of sterile workers, all of it funds this one afternoon.

The winged ants come in two kinds. The queens are the big ones, packed with the fat and muscle they will live on for months. The males are smaller and lighter, and they have precisely one job.

A single ant going up alone would meet nobody and get eaten. So colonies of the same species read the same weather and fly on the same day, which means queens and males from different nests actually find each other in the air. Warm, humid, still conditions a day or two after rain will set a lot of nests off at the same time.

Going up in a crowd is also a crude kind of armour. Every gull, swift and starling for miles piles in to feed, but there are only so many ants a bird can eat before it is full. Fly in your thousands on the same hour and most of you get through simply because the predators run out of appetite. Hölldobler and Wilson's The Ants calls this predator satiation, and it only works if everyone goes together.

She mates in the air, sometimes with several males, and stores enough sperm to lay eggs for the rest of her life. Then she lands, and the first thing she does is reach back and snap off her own wings. (That shedding has a name, dealation, which is where this app got its own.)

From there she looks for somewhere to dig. In most species she seals herself into a small chamber alone and raises her first workers on nothing but her own body, living off her spent flight muscles and fat until the first brood can forage. It is a brutal way to start. The overwhelming majority of queens are eaten, dry out, or simply never find a spot before something finds them. The very few that make it are the colonies your grandchildren will be complaining about.

Because it is, fairly literally, a wedding. The word just means "of a marriage", and for most of these queens it is the only day of it they will ever get. Everything after is decades underground, laying eggs in the dark.

There is no single flying ant day. Different species want different conditions, and different towns reach those conditions on different afternoons, so a swarm in one place and a swarm fifty miles away rarely land on the same hour. What is real is a window of a few weeks when the odds climb for the common species, and a handful of days inside that window when they climb hard.

That window, scored from live weather and read out species by species, is what Dealate forecasts for your location. A reason to look up. Not a guarantee.

If you want the detail, the flight timetable covers who flies at which hour, and the barometer piece covers what actually sets a flight off.