The good news about spiders the size of ponies, especially on this low-gravity rock, is that they don’t weigh much. I mean, in general, spiders don’t weigh a heck of a lot, and even with the square-cube law in place. it’s hard for a spider to weigh as much as a pony. If their exoskeletons weighed as much as bone they wouldn’t have the strength to lift their own legs, so we’re talking much lighter weight material, multiplied by the low density of anything formed on Serendipity, the Planetesimal of Hollowness.
So maybe thirty kilos for a really big one.
Granted, when thirty kilos decides to drop on your head and try to bite your helmet off, it’s noticeable, but it would be so much worse, like over 100 kilos.
So hooray for lightweight arachnids and not falling horses.
Also, I need to figure out how to make ice packs.