Have you seen the cottonwood fallout before? Does it look similar to anything you have seen? Have you lived in the Dallas area for very long?
Yes, I have seen cottonwood fallout before. I have lived in Dallas for over a quarter of a century (over half of my adult life).
If it were spiders, it would still be incredibly unusual for that many this late in the year, and this was verified from northeastern Dallas to at least 120 miles SW. I'm still baffled.