From time to time, you may have noticed huge numbers of winged ants taking to the air around your property. In fact, this happens at many different points through a broad swathe of the year, generally from April to October. When exactly swarming ants appear depends on a number of different factors. As you might have guessed, the timing depends on the species. There’s a lot of variation in emergence times, even between closely-related species, because of evolutionary differences.
Having said that, the timing is also crucially dependent on local climate and weather conditions. With some ant species, you can reliably predict as to when they will swarm in the spring, within a week or two, on a nice warm day. In comparison, here in the Pacific Northwest, rather than on the first warm day, many populations of swarming ants make their appearances later in the season. Local pest control companies are aware of this difference, and treat ant colonies in our area accordingly.
But what’s behind this phenomenon? It all comes down to ensuring the survival of the colony, and the species. When you picture an ant colony, you might think of it mainly being occupied by workers—which gather food and build the colony itself—and more aggressive guardians, which protect it. But in order to perpetuate their colonies, ants also produce a distinct class of reproductives.
During a reproduction phase, when their populations have declined, ant colonies will divert some resources from worker production to the production of these reproductives. Reproductives are distinct in a couple ways. First, egg fertilization—or lack of it—will determine their sex, and their fate in the reproduction process they were born for. Second, reproductives have wings and are capable of flight. These are the swarming ants you see every year.
Swarming Ants Are a Sign of a Growing Pest Problem
Reproductives take to the air after their colonies wake up from reduced winter activity. That means visible populations of swarming ants tend to peak in late spring and early summer, depending on environmental conditions. Initially, male breeder ants will wake up, and intentionally rub off pheromone deposits around the entrances to the nest. This will then trigger female reproductives to follow them out a day or later, which is thought to reduce inbreeding.
Subsequently, many groups of swarming ants from colonies across a wide area will intermingle, from ground level up to several hundred feet in the air. This is when the breeding event happens. Each male ant will try to inseminate as many females as possible—because by then, it’s every ant for itself. The males then die, while inseminated females will burrow underground, attempting to start their own new colonies as queens.
Most of the time, new ant colonies take a year or more to start producing reproductives. But ant queens carry enough sperm to last up to 20 years. This means individual colonies can last up to 20 years, leading to many waves of reproduction and population growth. So, if you see swarming ants around your property, you should seek out ant control before you’re overwhelmed.
When to Expect Swarming Ants from Common Pest Species
In the case of carpenter ants, these breeder ants will be produced at the end of the year. They will overwinter in colonies, and then, when spring arrives, emerge over a single day—although the day varies by colony. Harvester ants, common in desert areas, are more likely to emerge earlier in the year when there is more moisture, and more food in the form of plants to eat. Odorous house ants emerge at the very end of May. Pavement ants show a very sharp peak of breeding activity in June. Fire ant colonies, however, have shown signs of breeding activity from January through September.
One thing that they do have in common though is that in large nests, hundreds or even thousands of individuals may emerge per hour. In some species, worker ants will even hold back early-departing reproductives until the time is just right. That timing is very precise, down to a specific part of the right day, which is largely governed by moisture content in the air. This is because wetter days make it easier for new queens to burrow into soil after being inseminated by males.
After arriving safely underground, the queens lay their first eggs, metabolizing their fat reserves and muscles to feed this first generation. Some of these new ants will also eat other eggs before they hatch. After the first generation grows into workers, the will assist the queen in raising new generations of ants. But very few queens will get this far, as the mortality rate is very high among reproductives.
Now that you know what swarming ants are, you’ll know what is happening the next time they turn up around your home. Keep that in mind if they crash your next backyard barbecue!