bogleech:

People barely knew anything about barnacles in Darwin’s day, so when he discovered one that had never been documented he became interested in just what they were and how they related to one another.

Discovering that they were in fact incredibly specialized arthropods - something that nobody had even taken the time to notice - he became fascinated by what they meant for evolution theory and thought he’d take a brief detour to study them even further.

One thing lead to another and this turned into almost a whole decade of writing on barnacles alone. His mental and physical health infamously declined as he overexerted himself producing four gigantic volumes on nothing but the systematics of barnacle reproduction and adaptation, which to this day is one of the most detailed works on any group of animals ever.

As for the species he discovered that started it all his final words on the subject were “I hate a barnacle as no man ever has before.”