The accepted mode of getting otherwise unobtainable information is to go visit the cranky old hermit living in the mountains. It's just the sensible thing to do. So, naturally, everyone takes their monthly excursion to the hermit's hovel to consult him on everything, from lock-jaw to lovesickness, necromancers to nasal viruses.
Now, if everyone's always visiting the poor old hermit, there's going to be an enormous queue... "Wellcome to the Hermitt's Hovele, Please Take Ye a Number and Have Ye a Seate" reads the sign outside the packed dwelling.
Imagine the poor hermit, having retreated into the mountains to escape this precise situation...
Swordbiters are parasites. They are long, thin and silver, and digest metal, somewhat like rust monsters, but smaller and more insidious. They resemble stick insects, but when they cling to metal they are very well camouflaged, and one can be biting your sword for a week before you notice it. They cannot be removed by hand, as they are very strong, but if the blade is inserted into fire they will leap off to escape the flames. Sometimes, old treasure hoards are infested with them, and the first glimpse you get of the "glittering" weapons is a pile of rusted swords encrusted with these thin silvery insects.