Lava Spiders should generally not be attempted until over 20FS. This is dependent on skills such as [[weapon]] skill and [[shield]] skill as well as the quality of the equipment being used (armors and weapons).
Generally a 40-50ql armor set with a 50ql weapon and a player with 20FS can kill a normal lava spider if they keep their [[Focus]] level up. [[Mauls]] work especially well on spiders.
Always attempt to gain optimum footing whenever possible. Fighting on a [[horse]] is an excellent way of doing this.