Re: What causes ants from differents nests in the same area to fly same day?

You are right! Like bees, each colony has three types of 
ants...workers(nonreproducing females), queens(female) and Drones(male) 
Reproductive ants emerge in anticipation of rain as the humidity goes 
up...males and females take to the air to mate and get ready to establish 
new colonies.  After mating the queen loses her wings and sets out to dig a 
colony out and raise her first brood.  Since the queen is working alone, 
moisture makes digging easier, and keeps the first eggs from drying out until 
there are enough workers that can dig deeper chambers and move the 
subsequent broods around to keep them at optimum temperature.  Rains also 
brings out new plants if that's what the ants eat, helps grow fungus if the ants 
are fungus eaters, or new imature insects if that is what they eat. Moisture 
is vital to establishing a colony so when it rains there is no time to 
waste.  

 http://www.myrmecology.org/