When do you get behemoth biters?

[Nefrums]

Let me start by saying that I really like this game.

I am quite new to this game and I don't know so much. But after having launched a few rockets I have never seen a behemoth biter.

My last game was a 45+ hour game using marathon preset, and I still did not see a single behemoth biter!

My base generated about 1-2 science/s (including space science).
I did not use any extensive pollution minimizing tactics apart from eff1 modules in all miners.
But still after 45 hours and 15+ mining bases the biters where never a problem and not a single behemoth biter spawned.

Are behemoth biters only for the death world setting?

[Kayanor]

https://wiki.factorio.com/Enemies#Evolution

This wiki article holds some nice graphs and tables regarding enemy evolution and when behemoth biters will spawn.
Oh and the spawning of behemoth is not depending on the world preset setting, you can get behemoths on easiest settings, too.

[Jap2.0]

When you type /evolution in the console (it opens with ~), what do you get?