Answer:
I am a desire to munch
I destroy your home from the inside out.
I am a sharp looking horse with a flaxen tail. The longer I run the shorter my tail becomes.
You can read me both ways I wear; One way it's a number reversed a snare.
As I went over London Bridge I met my sister Jenny; I broke her neck and drank her blood and left her standing empty.
No matter how little or how much you use me, you change me every month.