Ok. But you have been warned...
First the fruit is submerged in huge water baths, fully submerged for a minimum of 30 minutes. So anything alive would drown. The bananas are taken out and the hands (bunches) are cut from the stalk, inspected for spiders and packed into plastic bag lined boxes, which have the air removed and are sealed. (so no oxygen) The boxes are loaded into shipping crates and held at a temperature of about 13 degrees which is too cold for tropical species to survive for the trip over here which takes around two weeks.
On arrival here the bags are ripped open and they are placed in ripening rooms where the pressure is equalised then ethylene gas is introduced. The rooms are airtight at this point. The ethylene gas starts the ripening process and co2 is released as a by product making the air in the room unbreathable. After 24 hours-ish the room is vented and opened up, and the fruit produces its own supply of ethylene gas to keep the ripening process going.
Finally the fruit is quality inspected. Ironically given the number of people saying only buy loose, it’s the bagged fruit that is individually inspected when it’s bagged by hand. The loose is fast checked, so only a certain percentage is checked.
Very occasionally dead spiders are found in the boxes. These sent for identification, and if tropical, they are reported back to the farm the fruit originated from and their systems are checked to ensure procedures are being followed to prevent this.
Live spiders are extremely rare, and almost always uk species. The only live tropical spider I ever saw was half dead, and only the size of a 5p piece.