i think part of what they wanted out of vagrants was to get the player to hear some weird bug noise and start looking for the source:
https://streamable.com/5v0pel
dark souls 1 actually had really good sound design.
this type of vagrant is likely to be way more rare than the crab version because the crabs spawn when people lose bloodstains with 5+ humanity and the orb ones spawn when you drop certain items.
the orb version is pretty common if you're in a high-traffic area where people gravelord. because once you hit 99 eyes of death you drop the rest and they are one of the items.
https://imgur.com/a7zbPmp.gif