This morning, in the back yard, the ants swarmed. The first picture shows the main cluster of the swarm, the posts in the background are railroad ties, which are about nine inches wide. The swarm footprint is a semicircle cut from a circle about 18 inches in diameter. There was no obvious reason why the ants were swarming. My son asked repeatedly why, and the best guess I could imagine is that two colonies were embattled.
None of the ants had wings, and there was no broad spreading of the swarm. Within two hours all that remained were a scattering of ant carcasses, the bulk of the swarm moved somewhere. This afternoon I will introduce them to boric acid. If you listened carefully you could hear the noise of all these ants moving, which was really surreal.
I do not know the species of ant nor their principal food. They were unaggressive and live in an area of the yard with abundant dirt and plants, it could be they are vegetarians. They do not seem to be damaging my plants, so it could be they are aphid ranchers or perhaps they just eat other invertebrates.
I Googled for “ant swarm” and other related terms; unfortunately, the bio-inspired “swarm” or “ant” algorithms for global optimization of undulating multivariate function spaces have poisoned Google for entomology. I had nearly the same experience with the Big Bee. If you have any thoughts or links, please post them as I am still quite curious. I would like to know why they might have been swarming, and anything interesting about the kind of ants.
Update late the same day
The ants came back in the evening. I noticed them around eight PM. They formed a larger and deeper mound than I saw this morning. Is this diurnal behavior? I have interfered in the research possibility by dusting them liberally with boric acid. I am unlikely to see them swarm again.