At the start of the game arachnophobic gets a message saying “THERE IS A SPIDER IN _, BEAT TO AVOID THAT AREA…” When arachnophobic goes to certain parts of the map, they get practically 0 vision for 10 seconds, and their vent or kill cooldown if applicable is reset to its start, as to punish them for going there. Cooldown of 10 seconds for going to that spot. This forces them to take the long way around in most scenarios, without making it impossible to go through.
These parts are
Skeld: the hallway connecting storage and cafeteria
Mira: The locker room.
Polus: undecided.
Airship: Engine room.