Great tactics, folks!
It was handy to leave Feanora as a frog, this increases attack of spiders by 100%.
Hint: Kiss her only after the battle
I managed to beat the giant spider with a Level 15 hero using:
Dwarves (High morale)
Cannoneers (High morale)
Giants (High morale)
Miners (High morale)
Alchemists (High morale)
It was a rather tough battle and I lost many troops, using "frog-shaped" Feanora and using Giants instead of hyenas ("earthquakes" are handy for those hordes of spiders) did the trick.
I also tried to attack the spider queen as much as possible, except for the giants who earthquaked or hit some spider troops.
Not a very original tactic compared to your results, but maybe some additional hints...
Cheers, gogol