Why Moths Have Powdered Wings

There is a cool spider living in a web outside my rear garage door. I watched it grow up from a little tiny thing to a pretty large cool looking spider. I wish I could get a picture, but my camera won't focus right. I've got to duck a little to avoid this spider's web, but that's ok. I figure that it catches all kinds of flying pests and eating mosquitoes is cool with me. The other night I was out back at night and I saw a moth. I caught it and threw it into the spider web in hopes of watching it get wrapped up by my friend, the spider. To my amazement, the moth didn't stick to the web. That's when I realized that they probably have powder on their wings for a reason. Maybe one reason is so that they don't stick to spider webs.