These recently-hatched cross orbweaver (Araneus diadematus) spiderlings appeared on the side of my house a few days ago.  They cluster like this for a few days, and then disperse.  I assume they must have an enormous mortality rate, or else my yard would be impassable for all the webs in late summer. They seem to find my house a hospitable spot, as I had a group hatch around my screen door last year.