Seems like a fun topic. Let's use the classic pain scale of 0-10 to rate pain so we can quantify it. I like this description from the Obstetrics unit in the hospital. Might not fit because it's for labor but it's fine.
0 being no pain
3 is uncomfortable
5 being moderate pain, clenching fists, obvious distress like sweating, change of breathing pattern
7 is so much pain you'd probably kill just to relieve some pain
9-10 is the worst possible pain anyone can ever imagine.
Pogonomyrmex subnitidus
I went anting a couple months ago and saw this giant Pogonomyrmex nest. I wanted to take a picture of it so I did. Well turns out there were more workers walking around than I thought because I felt this sharp pain on my Achilles tendon. I was wearing jeans so it was hard to get under there and remove the ant so I just squeezed from my knee to my shoe and scratched hoping to kill it. It worked out and the ant fell out.
5 minutes in and it's a sharp stinging/stabbing pain. The initial bite was a 3/10 right away. No big deal right? Well over the course of an hour it got worse and worse. An hour later it's about a 5/10 pain. The bite was the size of a marble and there was an obvious red bump there. It wasn't that itchy but it was an awful burning sensation.
This went on for about 6 hours and the peak of the pain was around 6/10. I didn't want to walk and I almost wanted to just stop moving and sit down. At about 8 hours it started to hurt less but it was now the size of a large grape. After that it was just an uncomfortable bump with some pain in my heel. It took around 9 days for the bump to go away but it was probably due to location, we don't have a lot of circulation in the area of the bite so healing was probably longer than it would've been somewhere else.
I experienced this bite on my heel, I can't even imagine what Nurbs went through.
Solenopsis invicta
Had a colony where I wanted to see just how fast this species actually grew. Needless to say they grow faster than expected. They broke the 500 worker mark within months and the test tube was halfway full of larva. Started starving them and got rid of it but not before I got stung on my right middle finger, the first joint past the knuckle.
Pain was meh, only about 2/10 stinging type pain. Except it was the itchiest thing in the world. It didn't form a pustule, a pus filled bump, but it was still itchy and red. The redness didn't form a half circle like the Pogonomyrmex sting did but it was still elevated. It was probably the size of half a penny. The area was slightly raised and red. I soaped the area for 5 minutes with warm-hot water so I think it helped with the bite.
It healed in a couple of days but it was itchy the whole time.