If you have Orsinium then Old Orsinium. Not only grinding exp is good there 4-8% exp per mob group and fast-ish repsawns, but there are an unholy amount of spiders.
I've accumulated like 700 spider eggs from there.
Difficulty scaling is desperately needed. 9 years. 6 paid expansions. 25 DLCs. 41 game changing updates including A Realm Reborn-tier overhaul of the game including a permanent CP160 gear cap and ridiculous power creep thereafter. I'm sick and tired of hearing about Cadwell Silver&Gold as a "you think you do but you don't"-tier deflection to any criticism regarding the lack of overland difficulty in the game.
If you dare venture into Imperial City, I found that spider eggs dropped quite regularly on the spiders in the AD side of the sewers. Got about 50 in an hour.
What faction are you? There's a delve full of spiders in auridon if it's one of your silver or gold areas. I forgot the name of it though.
Entila's Folly. Cave full of spiders and in the back there's a room full of quickly respawning wasps. I'm AD and I leveled up WW in about 30 minutes just devouring low level wasps. Would probably make a good grind spot for Cadwell's silver and gold.