First of all, if you are buying them, I suggest you choose bigger ones, so that after boiling they are more than just the peel.
If that's how you get them from the tree, that's it, you make them the way they are.
So, wash well and drain the sour cherries - if you notice any worms, leave in salted water for about an hour and you have solved the problem. Only make sure to rinse them thoroughly afterwards :)