Black crazy ants evacuating temporarily?

[BleedingRaindrops]

There's a Paratrechina longicornis colony living in the concrete right under my feet while I'm on guard post, so I like to watch them sometimes. Yesterday after it rained I noticed them rushing out of their main entrance in droves. Then some of them began carrying brood out, and then a queen emerged. I was excited when I saw the queen, because I had been wondering what they look like, since black crazy ants tend to reproduce inside their own nests, so the queen almost never has to leave and it would be nearly impossible to catch one.

I followed them to a small crevice in the wall created by the natural architecture of the building. Basically there's a decorative pocket in the wall that's hard to slip one's fingers into and is protected by piping anyway. They congregated there, and the queen moved about the established nursery tending to different ants here and there. Then another queen emerged from the nest and scurried back and forth along the established highway. I was amazed. I didn't know this species was polygamous. It was difficult to tell if she was directing the workers or vice versa, but she was constantly surrounded by about ten or so workers paying sole attention to her.

After a while the flow died down to a trickle, and there were about 200-300 ants congregated around that one little crevice, with a lot of brood (but no alates). They sat there for about ten minutes, with just one or two workers running in and out of the nest, and then, they just all started rushing back in. The workers always surrounded the queens as they moved, and after another ten minutes the whole colony was back inside their nest.

Does anyone know what might have prompted this? I've actually seen them do this a few times before—the whole colony, brood and all, outside the nest for a short time—but not always on a rainy day. I almost wonder if I could find a way to trigger it and then capture them as a colony, but I'm not currently equipped to house a colony of this size. Plus, I like to watch them while I'm on post, and I would be robbing myself of that. Still, I am curious about why they do this. Does anyone know?

[SpeciesK]

I don't know enough about ants to know anything, I don't even know where crazy ants are from, I am just speculating. You said there are pipes blocking the area. I wonder if there is hot water (or cold) that goes thru the pipes on a regular basis so the ants know "It's time for the hot water! We better grab our grubs and stand outside for twenty minutes until it cools back down!" So they are not so crazy after all, they can tell time!

[shaky33]

Theres probably a good chance they were heading to some sort of satellite nest but could not get to it for some reason. The water from the rain made them evacuate their main nest so they went to the next best thing.