Crawl reflects speed and creep sound. For example, a baby crawls. It goes slowly across the ground, but, of course babies are noisy. A burglar (Trying to rob your house) would be very quiet but would want to move faster, so he would creep.

In addition to Michael's excellent answer a "crawler" has 3 meanings: 1) a thing that crawls or moves at a slow pace, especially an insect. 2) someone who tries to curry favour with someone for their own gain. 3) a program that systematically browses the World Wide Web in order to create an index of data. and a "creepy crawly" is an insect, especially one which frightens people.

'To creep' means to go quietly ("He would creep into the building without anyone knowing"). It can also be an insult ("You creep!") usually to refer to a man being perverted; this meaning is a shorter way of saying 'creepy'. 'To crawl' means either to go slowly ("His pace slowed to a crawl"), or to move while on the ground ("You crawl along the floor"). 'To creep around the house' means you do it quietly. 'To crawl around the house' means you are on the floor, or moving very slowly.