Mageripper

Magerippers were tiny, utterly bizarre aberrations that both sensed and fed on magic, much to the detriment of any spellcasters in their vicinity.

Ecology
Mageripper swarms were among the creatures found in the sewers of Waterdeep, and they had also been reported living in Skullport. Additionally, the Thayan enclaves established by the Red Wizards often contained many magic items, making such places magnets for mageripper swarms, and keeping the swarms under control was a constant concern of the Thayans.