What is the success rate supposed to be for biter probes? I feel like I'm maybe getting one spawner for every 20 or 30 probes, which is really frustrating. I'm firing them near fish and trees, and there is more than 80% oxygen. Is it just supposed to take a lot of probes?

In fact, in general, the probe success felt a little too random for everything except algae and grass. It was pretty easy to get algae and grass to work as expected, but I wasn't able to figure out why sometimes I would get worms and sometimes not. Sometimes I would get trees and sometimes not. And with fish it was even more chancy.

In fact, I didn't really have all that many places where the algae grew and the fish grew and the worms grew and trees grew, and it seems like you need all those for the biter nests.

Is there some dependency on the underlying soil that I am not seeing?

If your success rate isn't good, then try layering on more fish and trees. If the oxygen is only just barely over 80, then maybe get it even higher for better results. You can use the terraforming and excavation drones to create islands that are surrounded by fish and dense with trees, and this has the added benefit of keeping them from being able to attack you.

OK. It wasn't clear to me that I should make the trees and fish more dense in pockets where I want the biters. I kind of just spread all my terraforming out instead of trying to make dense pockets. Thanks.

By the way, do they attack me? They don't seem to be expanding in any way. Yet. I did notice that if I walked my spidertron into their attack radius they would attack.

-- edit. nevermind. I went back to a spot where I planted some and they had expanded.

Pollution is not on by default, so they shouldn't be too aggressive, but they will gradually expand, and if they come into contact with your factory they will attack. Thus islands can keep them contained.