Instructions
Complete the game's first four missions. You will gain access to the Keeper Compound.
Enter the Keeper Library and talk to Artemus. You will receive a new objective to read a letter from Inspector Drept.
Read the note on the table beside Artemus. It will contain instructions asking you to kill the mites. You will receive the Hammer Blessing, which gives your arrows the ability to kill the mites.
Approach a mite. You can find them all over the City, including the South Quarter, the Docks and Audale.
Press your keyboard's "3" key to ready a broadhead arrow in your bow.
Aim your bow at a mite and click your mouse. The arrow will strike the mite and it will explode.