Crawling would be essentially what Google, Yahoo, MSN, etc. do, looking for ANY information. Scraping is generally targeted at certain websites, for specfic data, e.g. for price comparison, so are coded quite differently.
Usually a scraper will be bespoke to the websites it is supposed to be scraping, and would be doing things a (good) crawler wouldn’t do, i.e.:
- Have no regard for robots.txt
- Identify itself as a browser
- Submit forms with data
- Execute Javascript (if required to
act like a user)