Why do some spiders shake their webs?

Question

i have a spider outside that i find interesting to feed. whenever i throw a grasshoper into its net it will sometimes shake its web. why does it do that?

Answer 1

They shake the web violently when alarmed.

http://ohioline.osu.edu/hyg-Fact/2000/20...

Answer 2

To help it locate the object by the vibrations, also to help identify it, and to adhere it more securely to the web.

Answer 3

because you threw something on it dumbo