This came up tonight...What do you do with them?
Here you go.....
When you talk to Squire Rale in Necropolis, he will ask for powder that you get by combining various scarabs you get from the Necropolis Quests. You can combine them in the Stone of Change by the marketplace bank. Then take the powder back to him to claim your reward.
The Bloody Crypt yields
Charred Scarab, Crimson Scarab, Twitching Scarab, Ruddy Scarab, and Bloody Scarab.
Combine them to make Scarlet Scarab Powder QTY 1 each *confirmed*
Rewards
Lumric's Longbow +2 longbow w/ ghost touch *confirmed*
Touch of the Silver Flame Trinket grants lesser undead guard
Signal of the Silver Flame Trinket yields 2 extra turn undead attemps per rest
The Shadow Crypt yields
Shadow Guard Scarab, Shadow Knight Scarab, Shadow Lord Scarab, Shadow King Scarab, and Shadow Scarabs.
Combine these to make Dark Scarab Powder QTY 1 each *confirmed*
Rewards
Signet of the Silver Flame Ring Lesser undead guard and +2 to both CHA & INT
Morleths Docent gratns Wizardy II and acts as a Lesser Arcane sigil
Righteous Bracers grats Lesser undead guard and False Life
*note* sometimes the mummy in the Shadow King series will not yield scarab.
The Cursed Crypt
Blighted Scarab, Forbidden Scarab, Tormented Scarab, Unhollowed Scarab, and Cursed Scarab.
Combine these to make Eerie Scarab Powder QTY Unknown *still collecting*
Reward
Ghost bane Longbow +2 Long bow ghost touch and undead bane
Kaelth's Touch trinket w/ Undead guard and damage reduction of 5/evil
Dalorent's Seal Large +3 shield granting 2 turn undead per rest, after resting Devotion III,
Brillance III and is Sacred
Beignin's Breath trinket grants Wizardy III and Efficacy VI 3 times per day.
I can't guarantee the voracity of all this info, but I can say the Heart series is correct.