Magma Crawlers are small, four-legged little critters found in Antlion Overlord Pyramids. They serve no purpose other than to increase the dungeon difficulty and to provide Magma Crawler Eyes for the Antlion Overlord Pyramid internal puzzle.
Eight eyes are required for one part of the puzzle; be sure to stock up. The eyes serve no other purpose at this time.
Magma Crawlers have a neat trick up their metaphorical sleeve, however; they are capable of crawling on walls and ceilings, unlike any other mob in the game (unless you have a mod that provides similar).