为什么这么多的ASP.NET开发服务器实例？

I am debugging a large web application solution, with the main web application project as a single startup project, configured to use IIS for debugging. Whenever I run this application inside Visual Studio 2010, I still get multiple instances (sometimes over 15) of the ASP.NET Development Server starting up as well. Why does this occur? I am debugging a large web application solution