use  1-2  cleanser  and/or  1  healer  champion  for  the  spider.  

I have done over 50 test runs on the Nether Spider.

I have found the 5 man set up to shut the Nether Spider Down. 

- Block Damage

- Healing

- Shielding

- Cleansing

- Single Target Damage Dealing Hero / Poison Hero / HP Burn Hero / Enemy Max HP Nuke Hero

Your team health should never drop below 50%.

If your health drops below 50%, you have lost the battle.

The Spider will do tons of Poison damage.

The Poison damage is unavoidable.

What you must do is recover your health so much that the damage from the Poison will never surpass the amount of recovery your team will generate.

I have tried the following winning set ups against Hard Mode - Nether Spider - Floor 60:

Team 1:

- Roschard the Tower -----> Block Damage

- Vrask ---------------------> Healing

- Zelotah -------------------> Shielding

- Mausoleum Mage -------> Cleansing

- Frozen Banshee ---------> Poison hero

Team 2:

- Roschard the Tower -----> Block Damage

- Vrask ---------------------> Healing

- Arbiter -------------------> 2nd Healer

- Mausoleum Mage-------> Cleansing

- Rotos --------------------> Single Target Damage Dealer

Team 3:

- Roschard the Tower -----> Block Damage

- Vrask ---------------------> Healing

- Gorgorab ----------------> 2nd Healer

- Mausoleum Mage-------> Cleansing

- Steelskull ----------------> Poison Hero

And that is all

Still struggling here, can't keep my cleanser alive long enough, may try and rank up Grunch Killjoy

I read somewhere that I should avoid damaging the spiderlings, is this true?  Would damage include leech debuff or reflect damage?

Right now my team is:

Attack -- Turvold

Healer -- Flesh-Tearer

Healer -- Sinesha  (primary attack is all enemies, problem?)

Cleanser -- Reliquary Tender

Block dmg/shield -- Drokgul the Gaunt

Remove sinesha, her aoe makes ants attack you and when they attack they heal big spider. Scyl of drakes is great if you have her. Heals, revive, single attack, croud control. If you have aoe hp burn thats great too. 

Do you have any AOE buff strip? Once you take the spiderlings' counterattack away, things become drastically easier and you can AOE nuke. Reducing the big spider's turn meter helps too - they limited how much you can reduce it, but you can still delay her. 

I would suggest to use reliquary tender as your main healer (as mentionned above) or if you're lucky enough to have pulled a lord champfort he can be built to solo that boss.