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Hear me out. The pebbles are difficult to manipulate at our small size without large amounts of energy, correct? So, when we have our labor for- I mean, children, they will need to be taught how to dance. So, we divide them into pairs, teach them the basics, and then have them practice. However, we'll need to manipulate the dance to better distinguish our new empire. So, when they finally get the hang of it, we have them tie strong pieces of web between their dancing legs, and then put a pebble in-between them. Their constant dancing will sand the stone down into a proper wheel. Imagine it; a spider mass production line for the wheel.