Loki

As he opened the door to go out, a large black insect flew in. It was not a horsefly and it was not a deerfly; it was bigger than either. It flew in and circled the room in a malicious way.

[...]

The large black fly—it was the biggest, blackest fly you have ever seen—landed on the back fo Brokk's hand.
Both of Brokk's hands were on the bellows. He did not stop pumping to swat at the fly. The fly bit Brokk, hard, on the back of the hand.

[...]

The black fly circled the room thoughtfully, then landed on Brokk's neck. The insect stepped aside daintily to avoid a rivulet of sweat, for the air was hot and close in the forge. It bit Brokk's neck as hard as it could. Scarlet blood joined the sweat on Brokk's neck, but the dwarf did not stop pumping.

[...]

Loki, in fly shape, decided that there was no more time for subtlety.

[...]

Loki landed between Brokk's eyes and started to bite the dwarf's eyelids. The dwarf continued to pump, his eyes stinging. Loki bit deeper, harder, more desperately. Now blood ran from the dwarf's eyelids, into his eyes and down his face, blinding him.
Brokk squinted and shook his head, trying to dislodge the fly. He jerked his head from side to side. He contorted his mouth and tried blowing air up at the fly. It was no good. The fly continued to bite, and the dwarf could see nothing but blood. A sharp pain filled his head.
Brokk counted, and at the bottom of the downstroke he whipped one hand from the bellows and swiped at the fly, with such speed and such strength that Loki barely escaped with his life. Brokk grabbed the bellow once again and continued to pump.
"Enough!" called Eitri.
The black fly flew unsteadily about the room. Eitri opened the door, allowing the fly to escape.