crawler

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One that crawls, especially an early form of certain insect larvae.
• noun A vehicle, such as a bulldozer, that moves on continuous belts of metal plates.

from The Century Dictionary.

• noun One who or that which crawls; a creeper; a reptile.
• noun A dobson or hellgrammite; the larva of a neuropterous insect of the family Sialidæ, as of Corydalus cornutus.
• noun Also called clipper.
• noun A person or thing that moves slowly; particularly, a cab that moves along a street very slowly on the outlook for a fare.

from the GNU version of the Collaborative International Dictionary of English.

• noun One who, or that which, crawls; a creeper; a reptile.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Australia, obsolete A person who is abused, physically or verbally, and returns to the abuser a supplicant.
• noun Australia, slang A sycophant.
• noun A child who is able to creep using his hands and knees but is not able to walk.
• noun sports A crawl swimmer.
• noun A tractor crawler, a motorized vehicle that uses caterpillar tracks instead of wheels.
• noun A software bot that autonomously follows connected paths such as webpage links.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a person who tries to please someone in order to gain a personal advantage
• noun a person who crawls or creeps along the ground
• noun terrestrial worm that burrows into and helps aerate soil; often surfaces when the ground is cool or wet; used as bait by anglers