The Collaborative International Dictionary of English v.0.48:

Crawler \Crawl"er\ (kr?l"?r), n.
   One who, or that which, crawls; a creeper; a reptile.
   [1913 Webster]

WordNet (r) 3.0 (2006):

crawler
    n 1: a person who tries to please someone in order to gain a
         personal advantage [syn: sycophant, toady, crawler,
         lackey, ass-kisser]
    2: a person who crawls or creeps along the ground [syn:
       crawler, creeper]
    3: terrestrial worm that burrows into and helps aerate soil;
       often surfaces when the ground is cool or wet; used as bait
       by anglers [syn: earthworm, angleworm, fishworm,
       fishing worm, wiggler, nightwalker, nightcrawler,
       crawler, dew worm, red worm]

The Free On-line Dictionary of Computing (30 December 2018):

robot
crawler

   1.  A mechanical device for performing a task which
   might otherwise be done by a human, e.g. spraying paint on
   cars.

   See also cybernetics.

   2.  An IRC or MUD user who is actually a program.
   On IRC, typically the robot provides some useful service.
   Examples are NickServ, which tries to prevent random users
   from adopting nicks already claimed by others, and MsgServ,
   which allows one to send asynchronous messages to be
   delivered when the recipient signs on.  Also common are
   "annoybots", such as KissServ, which perform no useful
   function except to send cute messages to other people.
   Service robots are less common on MUDs; but some others,
   such as the "Julia" robot active in 1990--91, have been
   remarkably impressive Turing test experiments, able to pass
   as human for as long as ten or fifteen minutes of
   conversation.

   3.  spider.

   [Jargon File]

   (1996-03-23)