We've observed swarms of pavement ants all over the neighborhood and found out via the internet that this is to send off the winged queens and males to start new colonies. Assuming this is correct, I still have a couple of questions. First, why do so many worker ants need to swarm? Does this serve a useful purpose, like distraction or something? They just seem to be going in all directions (and occasionally moving pine needles and things). Second, as I was crouching over one swarm the ants dragging the winged ants seemed to switch directions and pull the winged ants back into the nest. Would there be a reason for them to do this, like because of my presence, or some other prompt, or was it just a coincidence?
Hello Anne -- Thanks for writing the antblog with this question, which I think will be of broad interest to ant observers. It is true, as you say, that ants send off winged individuals to start new colonies. These mate away from the parent nest, often in a mid-air swarm composed of winged ants from many different home nests, thus ensuring outbreeding. After mating, males soon die, but the females go to a suitable nesting site, break off their wings, build a small nest, and attempt to raise a batch of workers and thus become a colony queen. Most foundress queens fail, due to predation, desiccation, fungal infection, etc., which is why ants send out so many winged females during the life of the colony.
Ant colonies invest a lot of food and energy into brood rearing generally, especially into rearing the large reproductive forms. So they protect this investment the best they can for as long as they can, up until the last moment, when the winged ants fly off. A swarm of worker ants can intimidate potential predators from approaching the winged ants, and when they workers detect a giant form or shadow (such as yours), they try to protect their winged brothers and sisters by dragging them back into the nest. They also do this when changes in weather (sometimes even a mere gust of wind or small cloud blowing over) indicate possibly unsuitable conditions for a successful mating flight may arise. The more healthy winged ants they can keep alive for the eventual mating flight, the more likely it is a particular colony's genes will make it into future generations of their species.
James C. Trager of the Ask Ant Team