To defeat the Harpie bug swarm, you require level 33 Slayer and a Lit bug lantern, which can be bought from any Slayer store. 25 Slayer experience is given when assigned by a Slayer master.
Charm Drop Rates
Wield a fast weapon and wear half-decent armour. Make sure you have a Lit bug lantern (worn as a shield) equipped, too. These bugs don't deal too much damage, so Lobsters, Salmon, or Trout are a good food to have when fighting them. This monster is good to train on if you want fast experience and a lot of Fire runes. Melee armour is recommended.
A Swarm Of Bugs.
Clue scroll (level-2), Starved ancient effigy
Coins (30-1000), Gold ore, Fire rune (30-90), Steel hatchet, Iron hatchet, Steel boots, Staff of fire, Adamant med helm, Death rune (3), Steel full helm, Jug of wine, Cake, Chaos rune (15), Nature talisman, Mithril chainbody, Rune javelin (5), Fire battlestaff, Gold charm, Green charm, Crimson charm, Blue charm