These spiders are aggressive toward each other (but not toward humans). They will attack each other if in close quarters, though many may inhabit the same structure or area at any given time. They are most commonly found in rafters and wooden structures in suburban and rural structures or areas, thus getting their name, "barn spider".
This spider was made well-known in the book, Charlotte's Web, with a particularly interesting point that the spider's full name is Charlotte A. Cavatica, and the barn spider's scientific name is Araneus cavaticus. Also, one of Charlotte's daughters, after asking what her mother's middle initial was, names herself Aranea.
When agitated (by a puff of air, for instance) these spiders sometimes bounce up and down in the center of their webs, possibly in an attempt to look larger and more threatening.