Why are these ants moving as a pack?
This is a really wonderful phenomenon. Ants disperse far and wide, but when one of them finds food, it brings it back to the nest, and in doing so leaves a pheromone trail. The next scout follows this trail, and finds the food, and then leaves a second pheromone trail over the first one. As this continues, the trail gets stronger and recruits new ants to haul off the bounty. You can have fun with this. Take your finger and rub across the trail to erase it. Or place a piece of tape over it. This will confuse the ants for a while, until they make a new pheromone trail. If you have some time, break up a potato chip, or some other bait, and put it on the cement. Watch the first scout find it, and then leave a trail behind. Soon there will be many.