Answer: Webbing is usually associated with spider mites, not moths. I wonder if the moths were feeding on the mites? Since spider mites like dry places you can discourage them by regularly hosing off your rosemary. Preying mantids are indeed good guys so you'll want to encourage them to remain in the garden. As soon as they discover the spider mites they should move to the rosemary and devour the pests. I think I'd refrain from using pesticides and let the beneficial insects reduce the population of bad guys.
Good luck with your rosemary!
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