Once the spiders get to a web site, they typically index most of the words on the publicly available pages at the site. Whenever you search the web using a search engine, you're asking the engine to scan its index of sites and match your keywords and phrases with those in the texts of documents within the engine's database. It is important to remember that when you are using a search engine, you are NOT searching the entire web as it exists at this moment. You are actually searching a portion of the web, captured in a fixed index created at an earlier date. It's hard to say.
Spiders regularly return to the web pages they index to look for changes.
When changes occur, the index is updated to reflect the new information. However, the process of updating can take a while, depending upon how often the spiders make their rounds and then, how promptly the information they gather is added to the index. Don't waste your time with a search engine trying to find late-breaking news. Search engines are the best means devised yet for searching the web. On the down side, the sheer number of words indexed by search engines increases the likelihood that they will return hundreds of thousands of irrelevant responses to simple search requests.