My old biology professor did her PhD on Guinea Worm Disease. She used to tell the nastiest stories about what it was like. Suffice to say I have a healthy fear of worms to this day.
Harmless in the sense that they aren’t dangerous, but they are capable of biting. Source: one was in my headphones a few years back and was biting my ear. I initially thought my headphones were just really itchy.
In my headphones!
shudders
I still check my headphones every time before putting them on now