Mageripper

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

Description
On average, adult magerippers were only long and weighed. They were eyeless, instead have circular discolorations marking the location of specialized magic-sensing organs. The legs were insect-like, the two tentacles vaguely like those of a displacer beast, and the body was conical with oversized, sharp-toothed jaws. Magerippers were sickly purple, blue, and/or pink in color.

Behavior
Magerippers were animalistic, solely concerned with finding food and breeding. They weren't intentionally destructive but they were highly erratic.

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.