Mother was not very happy about the roof coming off. I only had my phone with me to further invade her privacy, so the photo is not what it could have been.
She's a wolf spider (family Lycosidae) and the kids have just hatched. That's their empty egg case she's carrying behind her like a limp balloon. Once they hatch, they climb her legs and ride around on her back until they are big enough to go off on their own to hunt.
Field guide authors and nature writers feel the curious need to emphasize the "solitary" nature of the wolf spider, as if they were some kind of weird hermits in contrast to the normally highly gregarious arachnid clan.
Really? So carrying several hundred of your family members around as they jostle for position on your back for a good chunk of your own lifespan is not enough togetherness for any arthropod?