Abstract: A disposable trap for animals such as mice comprises a cap assembly which is adapted for one end of a receptacle such as a beverage can. The cap assembly includes a flanged end plate having an entrance opening in a lower portion thereof, and an opening cover. The opening cover has a lower portion which covers the opening in the end plate and overlaps the end plate around the opening to form a one way door, and a narrow elongate upper portion which functions as a leaf spring to urge the lower portion to cover the end plate opening after the animal has entered the trap. A groove formed in the end plate flange fits into a mating groove present on most common beverage cans to prevent unintentional removal of the cap assembly from the can. Bent over tabs may replace the flange, and bent down tabs may be provided to prevent rolling of the trap.