In the evening, they would pour out of the crevices in the stadium in search of their nightly repast. However, during the day they deposited prodigious quantities of guano on the bleachers while hanging sleepily from the stadium canopy. Maintenance crews had to pressureclean the stadium twice a day to make it habitable - or sittable - for the fans.
Although the bats were a nuisance in some respects, they were also a valuable resource because they consumed tons of pesky mosquitos. Without bats (the mammal variety), the Mets would be spending more on insect control and less on guano control.
A solution was found by building a new, wooden bat house in a swampy area behind right field. It is now home to some 15,000 bats. Meanwhile, the bleachers are guano-free and nature's mosquito control program is working efficiently and economically.