Blood Crawler

A Blood Crawler is a monster found often in the Crimson. It can crawl on the background walls freely in any direction, but will traverse the terrain like the player if there is none. It follows the Spider AI.

Trivia
Blood Crawlers appear to be inspired by ticks, given the bloody theme of the Crimson. Ticks are however invertebrates, in which case it makes little sense for Blood Crawlers to drop the Vertebrae item.