the counter to it is range attacks and companions basically anything that solved the problem giant cave spiders had in Fort mode would be the solution in adventure mode...outside of cage traps.
Preliminary testing indicates that spider people have [WEBIMMUNE], letting them walk through webs with impunity.
Testing in arena mode, spider people don't stop getting more ridiculous. They have [NO_PAIN], no bones to chip, no throat to strangle. That plus their ability to use a bunch of shields at once makes them absurdly robust, even with their small size.
Arena testing of elephant seal men against brown recluse men[Proficient in all relevant skills, each wielding an iron shortsword. Brown recluse man gets four shields, because that's how many adventurer brown recluse men spawn with] reveals brown recluse men win nearly every time. Elephant seal men's raw strength lets them pulp any body part even with blade slaps, but they can rarely land that hit somewhere useful and have a hard time getting past the shield wall. On the other hand, Brown Recluse men often fracture or chip bones when they hit and only have to get through ONE shield. Assuming control of the elephant seal man, I was able to win by getting a lucky hit on the weapon arm and then pulping all four shield arms. I also won as the brown recluse man by stabbing whichever body part was easiest to hit until my opponent gave into pain and then stabbing the head until I finally won. The brown recluse men still die a third of the time[Including straight victories from the Elephant Seal men] from post-victory blood loss. Giving the elephant seal man a hammer instead of a short sword didn't change matters much either, despite it being better suited to their awesome strength and size.
Giant tortoise men, on the other hand, performed significantly better, winning most of their fights against brown recluse men. The main cause of why appears to be their much increased resistance to giving in to pain. Whereas one strike would cripple an elephant seal man, the giant tortoise men seem much more resistant to giving into pain, perhaps because of how flippers are processed bonewise. With them, if neither side landed an immediately lethal blow, the brown recluse men would usually bleed out before they could get a fatal shot on their opponent. Interestingly, none of the giant tortoise men retracted into their shell whatsoever, unless I assumed control and made them do it. Giving both sides steel weapons favourised the brown recluse men, since they could now sometimes make the giant tortoise men give into pain. The giant tortoise men still won most of the time, however.
Giant tortoise men against elephant seal men is a toss-up though. Neither side has any real advantage, as far as I can tell.
Giant cave spiders, for reference, easily kill elephant seal men. I was able to defeat one as a giant tortoise man by retreating into my shell and waiting until the spider fell unconscious from exhaustion before killing it. Brown recluse men easily kill giant cave spiders.
These results demonstrate the following:
-Elephant seal men, while somewhat larger and stronger then giant tortoise men, are nonetheless less robust and more prone to giving in to pain.
-Brown recluse men, despite having many arms and numerous useful tags like [NO_PAIN] and [WEBIMMUNE], suffer due to their small size.
-Giant tortoise men are large, strong and robust with the potent ability to withdraw into their shell. All in all, pretty good with no glaring disadvantages.
Honestly, despite my personal preference for brown recluse men, giant tortoise men seem to be the best here.