crawler · noun1
From crawl (“to move slowly, by dragging the body along the ground”) + -er.
crawler · noun2
From crawl (“to act in a servile manner”) + -er. From the Australian convict period (1788–1850); a prisoner who was purposely and extensively abused by an overseer (also a convict) and thereby driven to escape but who, finding it impossible to survive in the Australian bush, surrenders to this overseer, who would then have his penal term reduced. The particular crawler was picked for his weak personality and might escape and return a number of times increasing his own penal term each time. According to James Tucker, some convict overseers had their sentences extensively reduced using this odious practice.
Etymology from Wiktionary, CC BY-SA 4.0.