A crawling system crawls a web site initially in a pattern detection phase and subsequently in a pattern usage phase. The pattern detection phase attempts to identify patterns of references to pages that contain informational content of interest and patterns of references to pages that contain little informational content of interest. During the pattern usage phase, the crawling system crawls the web site. When the crawling system encounters a reference contained on an accessed page, the crawling system determines whether the reference matches a reference pattern. If the reference matches a reference pattern associated with pages that contain informational content of interest, the crawling system accesses the referenced page. If, however, the reference matches a reference pattern of pages with little informational content, then the crawling system discards that reference without accessing the referenced page.