Destroying prefab clones after they have fired?

I have made a robot which shoots spheres.

I did this on the iphone and in the arena he is in the spheres just gather in the corners after i have shot them, how do i make them disappear after they have been shot?

http://unity3d.com/support/documentation/ScriptReference/Object.Destroy.html

http://www.unitymagic.com/shop/en/unity-advanced-tutorial-019-destroy-objects/

You make a script and attach it to the prefab. You can call it "autoDestructor.js" or something. It will destroy your prefab after "lifespan" in seconds has passed.

JavaScript:

var lifespan : float;

function Awake() {

Destroy(gameObject, lifespan);

}