Can anyone identify or point me to a source to identify some spiders?

These spiders are small (about 3mm body length) with bright yellow bodies, black legs, and a black patch on the very end of their abdomens. They also seem to be social, with a couple of dozen living in a common web. Alas, no photos. I have a macro lens for my 35mm SLR, but it uses film, not CCDs, so I can't get any pictures.