I have found this to be extremely informative - and disgusting. Neither one of us has had any unusual reactions to anything, so let's just hope that it means that we're OK. I will keep the keratin thing in mind.
Seriously, I have found them in all kinds of disgusting ways. They LOVE chocolate. They found some big solid pieces (solid easter bunnies and the like) and made little roads all over them. They got into the rice. They have been into the tea tins big time.
Fyi, they will eat straight through even the toughest plastic bags, even sealed professionally. Glass jars with tight lids are the only solution we've found that works.
We rent our apartment, and like the city of florence, the cabinetry is old. This means that there are a zillion places for these buggers to hide. It took 2 days to get them out the first time, and I'll still find one flying around every now and then.
I didn't know what they were when I saw them early on! I didn't think it was crisis time. However, as I saw them multiplying to the point where they were ALWAYS somewhere, I mentioned it to my hubby. He came into the kitchen, saw them fluttering about, and exclaimed with the placid, happy innocence of a child, "butterflies!".
I have tried to get him on board with me - when you see one, kill it - but I don't think he's swatted at even one of them.
We've been talking about getting a new kitchen installed in the fall. Not for the butterflies, but I won't be sad if they leave us in peace...