
The Lost Fleas quest requires you to find five Fleas in Hollow Knight Silksong, and they're spread all across Pharloom.
Finding them can be slightly tricky, as they're all located away from the path you follow to complete the main story. We’ll provide you with all five locations, though, allowing you to track their whereabouts. I have sequenced them in the order I found them, but you can adjust it based on your requirements (and yes, there are more than five).