Spider webs can be painted with spray paint and "captured" on a surface. You can put a REAL spider web on your guitar or motorcycle tank. I've captured webs on simple squares of corrugated cardboard, plywood, even a clarinet case! The pictures I have taken do not do these any justice. They look like intricately hand-painted webs!
Step 1: You Will Need
some corrugated cardboard,
spray paints: one light color & one dark color,
a compatible matte clear coat of some kind,
Step 2: Choose a "canvas"
I suggest you try this out a few times on cardboard, to get the process down, before you try putting a web on a 3 dimensional object. Cut a piece of cardboard 8.5" x 11". This is your "canvas" Bigger webs may need a bigger "canvas". I've seen webs out in the timber, bigger than me! Cut another piece 8" x 1". This will be a handle. Tape the smaller piece to the back of the larger piece, bending it and taping it to make a handle. The handle allows you to.....uh.....handle it. Paint the front. Flat black works great, but you can use any dark color. Keep this handy so you can find it when you need it. You might want to make two or three of these.
Step 3: Locate a Spider Web
This might be the tricky part. Look for a spider web that is not damaged, and is in a location where you do not care about paint overspray. The woods, if you have some. Do not try to grab a web from your open-all-night car window, no matter how awesome a web it is, unless you do not care about paint on your car. When you find a web in a good spot, run and get your "canvas". Set the "canvas" somewhere nearby, while you paint the spider web with your light color spray paint. (silver or white works good) (I'm sure by now you've figured out where this is going. I always apologize to the spider, and they WILL spin another web, and another, but three seems to be about their limit, after that the webs start looking rather... hasty. So please take just one web from any given spider, unless you like watching them get hungrier and hungrier.) Multiple light coats! LIGHT COATS! Don't sag the web down with a lot of paint, just dust it on. Dust it on.
Step 4: The Cool Part
After you have the web dusted with light color (it is drying rapidly, don't worry) pick up your canvas in one hand, and the clear cote in the other. Dust a coat of clear on your canvas, then push the "canvas" directly through the web, and viola! (you might have to help break the web from its attachment points as you push through- you are trying to STICK the web to the piece) Dust some more clear on and let it dry. Neato! Once you have your technique perfected, you can web everything you own!