Have you tried drenching the soil around your hostas with diluted household ammonia? Aim for 1-2% ammonia. This also kills eggs.
"Household ammonia ranges in concentration by weight from 5 to 10% ammonia."
So dilute that by 5 times or ten times:
5-10% divided by 5-10 = 1-2% by weight, effective on slugs & eggs
If you start with something lacking perfume, ammonia is pure fertilizer and used as such by some farmers. After the slugs have had time to die, you might water the area you sprayed, to dilute the ammonia further and wash it deeper into the soil where it won;t evaporate and be lost.
It might be wise to wash off the leaves of delicate plants if you hit them with 2% or stronger ammonia. Maybe with a hose sprayer on "mist". Many plant leaves don't mind being sprayed with 1% ammonia or weaker (according to what I've read on the Internet).
It's also a way to kill them if you're squeamish. Adjust the sprayer to "jet" and shoot them from a distance. Put out cardboard or wood planks at night. Slugs will collect under it. Int he morning, flip the board or cardboard voer and spray the slugs you see.
