I've seen a number of reports about rats on airliners, usually foreign airlines (Pakistan was one). But mice are almost anywhere, so I wasn't surprised to come across the post below:
This is a report about "mice LIVING on many of the aircraft of one of the largest US major US airlines, whose aircraft we used to fly on the "interchange" program that used to exist before deregulation.*"
In a later post, he says it was American Airlines.
"On one flight, one living in the front biffy climbed up the leg of one of our captains, climbed into his underwear, and as he was flailing wildly, bit him on his private parts. Fortunately he was able to corral the beast so he didn't have to do the rabies shots. Funny how ever after he was always known for that rather than for his great skill and cunning.
Now that airlines don't serve food on board, I suspect the mice have found happier lodging elsewhere. I can't speak for the "blobs" in the water tanks, however."