What’s with the ant swarms in sidewalk cracks in summer? (DragonFlyEye, 7/20/2012)
The swarming behavior we see is actually a moving party: whereas the ants would normally be content to stay in their burrows most of the time, when the colony gets to big or cannot be supported by the environment, it splits off with a new queen to form an entirely new colony elsewhere. That would be why you see them – not simply swarming – but trailing off in a certain direction. It is very common to see these moving parties during the mid-summer months specifically because of the extended heat of summer.