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Right on cue the Solenopsis xyloni have been swarming in Phoenix.

At eight in the morning, the new queens are climbing up grass stalks and leaves.

Any idea why the worker ants are standing on and huddled around the queens?

I'll give you a hint.

You might be able to spot two of the reasons near the center line in this blurry photograph.

I'm afraid this is the best shot I got of the aerial assault by phorid flies.

Phorid flies of the genus Pseudacteon are known to attack fire ants. They are commonly called ant-decapitating flies for the fact that the infested ant's head falls off during the final stages of the fly's development. Each fly lays her eggs into the adult ants. The fly larva hatches from the egg, and feeds within the ant’s alitrunk. Once the larva is ready to pupate, the ant dies and literally loses its head. The larva pupates in the cozy head, and eventually emerges as an adult fly to attack more fire ants.

Photograph from Wikimedia

There was a small cloud of the flies attracted to the activity of the ants. These phorids seemed to particularly target the reproductives, although other phorids I have read about target workers.

To give you an idea how small and fast these flies are, check the area around the beige leaf in the lower right corner of the second part of this video.

Have you ever seen phorid flies around swarming ants? If so, what species of ants?

Solenopsis xyloni reproductive prepares to fly.

William Morton Wheeler had this to say about swarming in Ants: Their Structure Development and Behavior (1910) page 183:

"When the hour for the nuptial flight grows near, a strange excitement pervades the ranks of the workers. At such times even the blind and etiolated workers of the hypogaeic species venture out into the sunlight and accompany the males and females to the entrance of the nest. The winged forms move about in tremulous indecision, but, finally venture forth, run about on the stones or climb about on the grass-blades till they have filled their tracheae with a plentiful supply of oxygen. Then they spread their wings and are soon lost to view high in the air."