An aedeagus is a reproductive organ of male arthropods through which they secrete sperm from the testes during copulation with a female

It can be thought of as the insect equivalent of a mammal's penis, though the comparison is fairly loose given the greater complexity of insect reproduction. The term is derived from Ancient Greek αἰδοῖα (aidoia) 'private parts' and ἀγός (agos) 'leader'.