Nowadays, most commercially spun knitting yarn contains a mothproofing ingredient.
–Margrit Lohrer, Morehouse Farm Merino Knits (New York: Potter Craft) p 33Makes me think of some vintage Mary Maxim wool yarn I saw in a Nanaimo, B.C. thrift shop. The label said it was treated for moths. I hardly ever look at commercial yarn but I was struck by the strangeness of a yarn label announcing the wool was treated with chemicals. Lohrer's point, I think, is that you need to be told what's on the yarn because mothproofing is unadvertised today. She goes on to say that her yarn is untreated. The unspoken conclusion is that she believes untreated wool makes for a better product.
I like for information to be on the label.