crawlers

Crawlers, Web Crawler, Web Spider, Robto Crawler, Robots, Bots, etc.

see Web crawler

Web search engines and some other sites use Web crawling
or spidering software to update their web content or indexes
of others sites' web content. Web crawlers can copy all the
pages they visit for later processing by a search engine which
indexes the downloaded pages so the users can search much more efficiently.

User-Agent list of active crawlers