One of the most disconcerting places to find ants in your home is inside of your refrigerator. If you find ants in your fridge, they're most likely common carpenter ants and they're probably seeking out some meats or sweet stuff.
While you may think you have a clean refrigerator, most of the bottles and jars and cartons all have some kind of residual foodstuffs on them that will entice an ant visit. Jellies and jams are definitely ant favorites, so you may find a trail of them leading to the mess around the sides of the lid. Meats are also on the menu, so anything not completely sealed will get some ant attention.