bicycle crunches Riddles

Every day, a woman was seen crossing the border carrying bags of sand on a bicycle. After some time, the border police become suspicious and stop her, but found she only had sand on her, so they let her go. Years later, they get a mysterious invitation for a party at a large villa. The owner comes out to greet them, it is the woman that has been crossing for years! How did this happen?

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?