Situated in the wing membrane of both sexes, it is significantly larger, more developed, and only functional in males.

During daily grooming, males actively fill the wing sacs with a composite mixture of urine, saliva, and glandular secretions.

During courtship, a male hovers in front of a female and rapidly fans his wings to direct the potent, information-rich scent mixture toward her to influence mate choice.

The liquid inside the sacs carries complex chemical fingerprints that convey individual identity, age, and other atributes that influence selection.

As a territorial defense males shake or flick the contents of the wing sacs toward rival or intruder bats outside of their harem territory to warn them off.