There's actually quite a dearth of information on this yōkai on the internet (but not the long-horned beetle, kamikirimushi). All sources pretty much say only one thing: this yōkai appears out of nowhere when a person is about to marry a yōkai/ghost/shape-shifted animal and attempts to cut that person's hair. Doesn't really say much, right?
Or does it? Nearly all references to cutting hair (with only a couple of notable exceptions) in Japanese literature refer to the cutting of hair in order to take a monk's or nun's vows. Imagine, if you will, you are at a nice Catholic wedding and the groom walks in wearing the collar and suit of a priest! Strange? Also, keep in mind that hair was worn long (especially by women--the hair of Heian era women reaching longer than she was tall in some cases), so to keep our little priest analogy more at pace with growing hair back out, let's just imagine the groom can't take of his priest's collar for at least several months. Something like this is likely to cause a big stir, possibly a postponement of the wedding, and people are going to talk.