A web scraper functions in data gathering by automating the process of collecting information from websites. It uses HTTP requests to access web pages and then parses the HTML content to extract relevant data. Scrapers can use libraries like BeautifulSoup or Scrapy in Python to navigate DOM structures and retrieve specific elements. Data collected can be stored in a database or a spreadsheet for further analysis. Web scrapers are invaluable for market research, price comparison, and other data-driven applications.