Long story short, a lot of things are happening on a map with no colonists on it.

I just planted some giant rice and corn fields, didn't really develop much past wooden walls and bedrolls, so I figured that I would just come back to it during harvest season and have a lot of food in the ground to support me on my return. This rationale was a consolation that I was giving myself over the fact that I just discovered and killed a sightstealer, but not before it could get off a shriek. I knew more were inbound, but since I had a window to escape, I took it. Not much long after, the horde of sightstealers finally arrived, invisible to the map. Then, some raiders from Muggug rolled up thinking that they would help themselves to my unprotected storage cache. Little beknownst to to them, they were mysteriously swarmed by sightstealers and ended. Then a nociosphere came, and once it went unstable, it teleported around killing all the sightstealers that were globbing up around it. (Every time it does this it kills maybe 2-3 sightstealers before going dormant again.) Then the blood rain came and drove all the animals wild, so the sightstealers emerged again to fight the animals.

I'll come back when the sightstealers have been finished off. I think it's going to take a couple years.