Answer:
With pointed fangs I sit and wait; with piercing force I crunch out fate; grabbing victims, proclaiming might; physically joining with a single bite. What am I?
What has feet and legs, and nothing else?
When I live I cry if you don't kill me I'll die.
You use me from your head to your toes. The more I work, the thinner I grow. What am I?
In my life I must bare my bloodline I must share.
I am rarely touched but often held. If you are smart you'll use me well. What am I?