As my neighbors watered the plants in our backyard, I watched ants boiling out of cracks in the brick patio, racing to escape the onrushing tides. Looking more closely, I discovered they were carrying tiny white bundles in their mandibles. I recognized eggs and larvae. The ants were rescuing their brood from a flood apocalypse caused by oblivious humans.
Later, when surveilling a trail of ants marching across my kitchen counter, I spotted one that was enormous—twice as big as a typical worker, with an elongated, bullet-shaped abdomen. I was watching a queen ant marching through my kitchen. The experience gave me chills; there was something genuinely awe-inspiring about seeing a queen in person. I had never heard of ant queens wandering around in the open. I guess I thought they were egg-laying machines, like the Queen in Aliens, and never left the deepest confines of the ant nest.
But spring isn't just about expansion. For Argentine ants, it's also time for their annual sacrifice. Hidden from human eyes, in shallow tunnels beneath tree trunks and underground, the worker ants kill 90 percent of their queens. By one estimate, the queens go from 30 percent of the population to less than five percent. It's hard to say why the workers would do this at the beginning of their mating season; Tsutsui called it "mysterious and bizarre behavior." So far, scientists have not been able to figure out whether this annual sacrifice changes the genetic makeup of the colony. It seems that the queens are killed with little regard for age, fitness, or genetic relatedness to the rest of their sisters.
After the queens have been executed, mating season begins.