Do creatures climb stairs?

General
1

Just curious if the local wildlife will climb the stairs to my treehouse? I know they can fall down mining holes, don’t ask my how.

2

they can jump up 1 block, but 2 keeps them out

3

Yes, the clever little critters can climb stairs and single blocks… except for the hoppers… they can go higher!

4

Thanks good to know. Guess I’ll need a door a some point.