Mating frenzies, sperm hoards, and brood raids: the life of a fire ant queen

By Walter R. Tschinkel — January 2020

It’s June, just after a heavy rainfall, and the sky is filling with creatures we wouldn’t normally expect to find there. At first glance, this might be a disturbing sight. But for the lucky males and females of Solenopsis invicta, otherwise known as fire ants, it’s a day of romance.

This is the nuptial flight, when thousands of reproduction-capable male and female ants, called alates, take wing for the first and last time. But even for successful males who manage to avoid winged predators, this mating frenzy will prove lethal. And for a successfully mated female, her work is only beginning.

Having secured a lifetime supply of sperm from her departed mate, our new queen must now single-handedly start an entire colony. Descending to the ground, she searches for a suitable spot to build her nest. Ideally, she can find somewhere with loose, easy-to-dig soil— like farmland already disturbed by human activity. Once she finds the perfect spot, she breaks off her wings— creating the stubs that establish her royal status. Then, she starts digging a descending tunnel ending in a chamber. Here the queen begins laying her eggs, about ten per day, and the first larvae hatch within a week. Over the next three weeks, the new queen relies on a separate batch of unfertilized eggs to nourish both herself and her brood, losing half her body weight in the process. Thankfully, after about 20 days, these larvae grow into the first generation of workers, ready to forage for food and sustain their shrunken queen.

Her daughters will have to work quickly though— returning their mother to good health is urgent. In the surrounding area, dozens of neighboring queens are building their own ant armies. These colonies have peacefully coexisted so far, but once workers appear, a phenomenon known as brood-raiding begins. Workers from nests up to several meters away begin to steal offspring from our queen. Our colony retaliates, but new waves of raiders from even further away overwhelm the workers. Within hours, the raiders have taken our queen’s entire brood supply to the largest nearby nest— and the queen’s surviving daughters abandon her. Chasing her last chance of survival, the queen follows the raiding trail to the winning nest. She fends off other losing queens and the defending nest’s workers, fighting her way to the top of the brood pile. Her daughters help their mother succeed where other queens fail— defeating the reigning monarch, and usurping the brood pile. Eventually, all the remaining challengers fail, until only one queen— and one brood pile— remains.

Now presiding over several hundred workers in the neighborhood’s largest nest, our victorious queen begins aiding her colony in its primary goal: reproduction. For the next several years, the colony only produces sterile workers. But once their population exceeds about 23,000, it changes course. From now on, every spring, the colony will produce fertile alate males and females. The colony spawns these larger ants throughout the early summer, and returns to worker production in the fall. After heavy rainfalls, these alates take to the skies, and spread their queen’s genes up to a couple hundred meters downwind.

But to contribute to this annual mating frenzy, the colony must continue to thrive as one massive super-organism. Every day, younger ants feed the queen and tend to the brood, while older workers forage for food and defend the nest. When intruders strike, these older warriors fend them off using poisonous venom. After rainfalls, the colony comes together, using the wet dirt to expand their nest. And when a disastrous flood drowns their home, the sisters band together into a massive living raft— carrying their queen to safety.

But no matter how resilient, the life of a colony must come to an end. After about 8 years, our queen runs out of sperm and can no longer replace dying workers. The nest’s population dwindles, and eventually, they’re taken over by a neighboring colony. Our queen’s reign is over, but her genetic legacy lives on.

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