So I'm trying to make a giant cave spider man adventurer (partially because I was too lazy to find the dragon or hydra entries)
would this code work?
When trying to design exotic creatures, its usually good practice to look for comparative creatures. I can tell you that your coding is 'misguided' but first lets look at what a 'aboveground' spider-person would look like.
[CREATURE:BROWN_RECLUSE_SPIDER_MAN]
[COPY_TAGS_FROM:SPIDER_BROWN_RECLUSE]
[CV_CONVERT_TAG]
[CVCT_MASTER:STATE_NAME]
[CVCT_TARGET:brown recluse spider]
[CVCT_REPLACEMENT:brown recluse spider man]
[CV_CONVERT_TAG]
[CVCT_MASTER:STATE_ADJ]
[CVCT_TARGET:brown recluse spider]
[CVCT_REPLACEMENT:brown recluse spider man]
[CV_CONVERT_TAG]
[CVCT_MASTER:SYN_NAME]
[CVCT_TARGET:brown recluse spider]
[CVCT_REPLACEMENT:brown recluse spider man]
[CV_CONVERT_TAG]
[CVCT_MASTER:SYN_IMMUNE_CREATURE]
[CVCT_TARGET:SPIDER_BROWN_RECLUSE]
[CVCT_REPLACEMENT:BROWN_RECLUSE_SPIDER_MAN]
[APPLY_CURRENT_CREATURE_VARIATION]
[APPLY_CREATURE_VARIATION:ANIMAL_PERSON]
[GO_TO_END]
[SELECT_CASTE:MALE]
[CASTE_NAME:brown recluse spider man:brown recluse spider men:brown recluse spider man]
[SELECT_CASTE:FEMALE]
[CASTE_NAME:brown recluse spider woman:brown recluse spider women:brown recluse spider woman]
[SELECT_CASTE:ALL]
[APPLY_CREATURE_VARIATION:PUNCH_ATTACK]
[APPLY_CREATURE_VARIATION:KICK_ATTACK]
[APPLY_CREATURE_VARIATION:MOUTH_BITE_VENOM_ATTACK]
[APPLY_CREATURE_VARIATION:STANDARD_BIPED_GAITS:900:711:521:293:1900:2900] 30 kph
[APPLY_CREATURE_VARIATION:STANDARD_CLIMBING_GAITS:2990:2257:1525:731:4300:6100] 12 kph
[APPLY_CREATURE_VARIATION:STANDARD_CRAWLING_GAITS:2990:2257:1525:731:4300:6100] 12 kph
[GO_TO_START]
[NAME:brown recluse spider man:brown recluse spider men:brown recluse spider man]
[DESCRIPTION:A person with the head and arms of a brown recluse spider.]
[POPULATION_NUMBER:5:10]
[CLUSTER_NUMBER:1:3]
[MAXAGE:60:80]
[CREATURE_TILE:'s']
[COLOR:6:0:0]
Where you have 'gone wrong' is that you've tried to umberella term giant cave spiders to a template that can't take them and make them usable in the desired way. The animal men templates are meant to be applied to savage biomes (as on the bottom of the variation code), and in this respect you can see in the raws for the subterrean that all animal men created below ground were done by hand. There are no savage biomes underground so its a little borked.
Doing this amphromorphisation of giant cave spiders lends itself to a number of creative avenues, you could create anything from nerubians (if you get the WoW reference) to spider-centaurians (people with the lowerbody of a spider, bodyglossed with abdomen and the upper 2 armed body of a human) etc. Whatever you wish as long as it anatomically and functionally works.
The first half of what you were doing prior to the creature variational token was entirely correct (if you want to identify it as 'man' anyway rather than a intelligent creature like a trogg/troll), i recommend asking further questions and doing a little research into making your own body types, so you can shortcut a template quickly for your giant cave spider, then tweak the size/relative sizes.