Leiobunum politum fits the harvestman (although I don't know much about these, so there might be other possibilities). Understory of swampy woods, & absolutely huge (easily 5 cm across, including legs).

But it's the red things that I was really fascinated by. Turns out they are parasitic mites. And bugguide.net/node/view/36531/bgimage gives the these as nymphs of Erythraeidae, genus Leptus.

I can't seem to get iNat to offer genus Leptus. External providers offer Subgenus Leptus (as well as various sp.), but that seems to be a plant, according to the icon.

These big harvestmen were found in the understory of swampy woods, & were easily 5 cm across, including legs. But it's the red things that I was really fascinated by. Turns out they are parasitic mites. bugguide.net/node/view/36531/bgimage gives them as nymphs of Erythraeidae, genus Leptus.

Spiders have 2 apparent segments (cephalothorax & abdomen); harvestmen (daddy longlegs) have only one. These were found in the understory of swampy woods, & were absolutely huge (easily 5 cm across, including legs). But it's the red things that I was really fascinated by. Turns out they are parasitic mites. bugguide.net/node/view/36531/bgimage gives them as nymphs of Erythraeidae, genus Leptus.