Spectacular swarms of flying ants are a common summer phenomenon. Sometimes
people will observe winged ants issuing in large numbers, pushed out by the
wingless workers, from a colony established between a sidewalk crack or in a
small mound. Other times only the winged forms will be seen, aggregating in
large numbers around certain prominent points in the landscape.
Some background. Ants are social insects. The colony is established through the initial efforts of a mated "queen", a sexually mature female. Originally winged, after mating she sheds her wings and the no longer used wing muscles are an important source of nutrients for her during the early stages of colony development. Very, very few queens successfully survive this period and establish a functional colony.
However, if the colony makes it through this period it can begin to grow. Wingless, non-sexually mature workers are reared which subsequently help expand the colony. After several years, the colony may be well-established and then some resources are put into rearing reproductive forms. These are the winged ants, some females - the potential future queens - and the majority males.
Periodically, usually following by 3-5 days a heavy rain, the winged reproductive forms emerge from the colony in large swarms. Such swarming behavior is usually synchronized by other nearby colonies so large numbers of winged ants suddenly appear. All mating for the species takes place, often over the course of a single day. The males die and the mated females disperse to attempt establishing a new colony.
One behavior associated with some ants during mating swarms is "hilltopping". This refers to their aggregation around prominent points of a landscape where they search for mates. A large tree, the chimney of a roof or even a tractor moving across the plains might serve as such an "action site" for swarming winged ants.
Although dramatic, swarming ants pose no harm or risk of increased ant infestation. Those seen emerging from a colony were always there and are in the process of leaving the colony permanently. Mated females amongst aggregating masses similarly disperse from the area.
However, in rare cases winged ants are seen moving into the house. In some cases it is likely that an established colony exists within the home and may need to be treated. Carpenter ants and pharaoh ants are two species that can produce a nest within a building.
Other ants, such as the field ants, commonly nest outdoors next to foundations and may incidentally swarm indoors, working their way indoors through foundation cracks. And harvester ants in the midst of hilltopping behavior may fall down chimneys. In these cases there is not risk of permanent household infestation.