According to a web site I checkd that listed every creature and its weaknesses Yagluth does not have a weakness to piercing damage like the rest of the Prarie creatures. The site recommended Frostner or anything else with good blunt damage.

Silver arrows might workbut Yagluth doesn't seem to take more than normal damage from spirit based weapons. but he seems to be set up to be effectivly immune to arrows.

Site i'm referencing;
https://www.slythergames.com/2021/02/23/valheim-enemy-weaknesses-resistances/