Harpie Bug Swarm requires level 33 slayer to be assigned as a slayer task. To be able to injure this creature, you must have with you a lit bug lantern, which also requires level 33 firemaking. You may be assigned this task even without meeting the requirement of 33 firemaking, and the assist system cannot be used to light the lantern, so in turn 33 firemaking is a requirement for this task. For every kill you will receive 25 xp in Slayer. Weakness to crush attacks (eoc)
Harpie Bug Swarm is located just North-East of the Tai Bwo Wannai village on the island of Karamja. Possible ways to get to this creature would be by using a Charter to Brimhaven, Karamja boat located in Port Sarim, Amulet of Glory teleport, and with level 57 summoning you can get to them using a Spirit Graahk.