An Axiom of Nature.
When a deer fly finds you, it becomes a epic struggle that can only result in one of three outcomes: (a) she bites you, (b) you kill her, or (c) she bites you and you kill her. They are the Kamikazes of Nature, and are justifiably loathesome.
Footnote: The feminine description is used because it is the females that bite. The males appear to be content with collecting pollen.