They do not make use of indexing software agents and so have no way of knowing it's out there. Directories are usually subdivided into categories and you have to submit your URL under the most appropriate heading. Even though your site may show up within a day or two, most of the search engines take time to list a site. If after the time listed in the chart above has elapsed and you are still not finding your site listed, you should re-submit your URL to the search engines that do not have your listing. It often takes more than one submission to get the best results.
Search engines receive tens of thousands of submissions every day.
On days when the submission level is above normal, a certain number of submissions can be received properly but still not get listed. If your listing is not appearing on a certain search engine, you should resubmit it. The critical pages to submit are your major topic pages, pages with unique content, or pages that describe a specific product or service. For example, a sports store will have separate pages on basketball, baseball and football which should all be submitted. In order for site visitors to easily navigate your site, these major topic pages should provide clear links to other topic pages and your home page.