A harp trap is a device used to capture bats without exposing them to disentangling from traps like mist nets and hand nets. It capitalizes on bats' flight characteristic of turning perpendicular to the ground to pass between obstacles, in this case the trap's strings, in which flight attitude they cannot maintain their angle of flight and drop unharmed into a collection chamber. Invented in 1958 by US Public Health Service veterinarian Denny Constantine, the harp trap has been modified for different applications and efficiencies by users, including Merlin Tuttle's double harp trap in 1974, Charles Francis' 4-frame harp trap in 1989, and other modifications improving collapsibility and portability.