It may feel like the Invasion of the Home Snatchers. You're ecstatic to see your college students they sweep in with enthusiastic independence and 4 weeks of dirty laundry. They descend briefly, eating you out of house and home. You can't wait to hear all about college (but their mouths are full.) They can't wait to spend hours on the phone talking to their friends.
Are they from another planet?
They may sleep until 2:00 in the afternoon and first start their social lives after midnight. (Definition of a teenager - a person who lives in your house, but functions in another time zone.) They breeze in, use your home as a refueling and landing pad, and breeze out.
Your college students probably expect that their home and family will have a museum-like quality with nothing ever changing. They don't realize that just as their lives are growing and evolving, their parents' lives can change too. College students are dismayed to come home and find the space and furniture re-arranged, their rooms or closets put to a different use. They're shocked that dinner isn't at 6pm anymore or that Mom never seems to be home.
You, as a parent, may start to feel resentful and ignored. They come home, and they don't quite act like members of the family, but they're not as well behaved as if they were guests. Don't worry; everybody goes through this.
Discuss Expectations
Make it clear that although you understand and applaud their new independence and their ability to take care of themselves, when they're under your roof they are part of an interdependent family, and everyone is accountable. So if you want to know what their plans are, where they're going and when they'll be home (which you have no idea about when they're away at school), you are not unreasonably invading their privacy. "Will you be home for dinner?" relates to meal preparation and table setting; it doesn't mean you want to take over and control their every movement.
If you clearly and consistently expect them to clean up after themselves, do their own laundry, or help with routine household tasks, eventually they will get the idea. It just takes time.
And if all else fails, remember: very shortly those home snatchers will be going back to school!