Originally posted by jamesc70:

They do give you a hint that 'it is dangerous at night'. If you are running around the Black Forest at night, then be prepared to be mobbed. As for mining at night, just build a wall around your copper vein... I've had tons of dwarves attacking my wall as I mine at night, and they rarely do 1/2 damage to any single wall piece, and you can repair it in an instant easily with the hammer.

https://steamcommunity.com/sharedfiles/filedetails/?id=2609041726

It's not at night that this is noticeable but during the day. I've trenched the area around a spawner but occasionally whole groups spawn outside of the area I have dug out.