so, as far as i can tell, tsuchigumo are the youkai form of japanese purse-web spiders (scientific name Atypus karschi if anyone wants to look them up,) and these guys build... kinda weird webs?
arachnus, being a tsuchigumo, builds the classic Atypus web structure: a horizontal silken tube about three times his length and large enough for him to move around reasonably freely inside. of course, purse-web spiders usually build their Tube in a burrow they've dug into the soil, but arachnus did not do that so his Tube is not hidden by dirt
when prey approaches the web, a normal purse-web spider will lunge, grab their prey through the silk, bite a hole in the web, and then drag their prey through. that is very annoying because it means every time you catch something you have to go back and fix the hole you cut in your house. so arachnus basically just made a permanent hole in the web sorta like a trapdoor so he can just reach out and drag his husband (toadal dude) in for snuggles without needing to repair the web after
(also if his web gets damaged, he will eat the damaged silk during repairs. it's a spider thing.)
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