How the ants could getin the pipe unless there is a leak somewhere is beyond me unless they entered through the shower head. Water piping is mostly a closed system. Even if they entered through an outside hose connector if it is shut off its sealed shut.

What a horrible experience. I am fighting ants on my farm constantly but I would be grossed iut by that too. I always run my hot water through the shower head fir several minutes before ever getting in.

Maybe if you run the shower head first to heat your water & let it just run down the drain then run the water into the tub you will insurw nithing comes out in that horrible shocking way again.

I learned the hardway not to eat in bed. Dang ants got in my bed & one ended up in my ear....yep, ants are a gross nuisance.