In Norse mythology, Loki took the form of a gadfly to hinder Brokkr during the manufacture of Mjölnir. He probably looked a lot like the fellow below (click for larger view).
Science classifies him as a male Tabanus atratus, a Black Horse Fly, first accurately depicted by Robert Hooke who “marvelled at the eyes of a “drone fly” in his Micrographia (1665)”.
I still think it was Loki.
Denney Home Place 
We also have these here in Illinois. Big ones! 🙂
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Scarily big!
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Their bites must hurt! We protect ourselves by spraying him. I think Thor laughs about it.
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