I found this myth in a wonderful little book. This explanation of the origin of midgies is perfect! I'm only sharing the absolute minimum of the myth so as not to spoil the story for those interested to purchase the book.
Malevolent Norse giant Thrim, hating humans and thinking of them as his favorite food, was expelled from Norway for causing havoc and disrupting the fragile peace between giants and humans. He left eating his way out of Norway to Shetland and then to Orkney chanting “I’m gonna find you. I’m gonna catch you. I’m gonna eat you.” From there he tromped through the Pentland Sound to Caithness where began to eat his way across the Highlands. He eventually made his way to Applecross. The good people of Applecross devised a plan to kill Thrim.
I’ll stop here, not giving away more of the story other than to say the people of Applecross were not entirely successful in their attempt to completely destroy Thrim as evidenced by little black midgies chanting “I’m gonna find you. I’m gonna catch you. I’m gonna eat you’.
This is a very interesting little book.
The Anthology of Scottish Folk Tales, compiled by David Smith