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.