I found this at http://www.ladybuglady.com
6. How can I get them out of my house?
A. If you don't have a lot, just leave them. They will leave when spring arrives. Disturbing them will only cause them to stress out leaving yellow markings on your walls. The yellow stuff, you see, is not waste matter, but rather, their blood. Ladybugs release a small amount of their blood which is yellow and smells, when they sense danger. Some people have said that it does stain on light colored surfaces.