Aedeagus

Aedeagus of water scavenger beetle Tormissus linsi

An aedeagus (plural aedeagi) is a reproductive organ of male insects through which they secrete sperm from the testes during copulation with a female insect. The sperm contains capsules called spermatophores, which contain the spermatozoa. In addition to the spermatophores, in some insect species the aedeagus also discharges a spermatophylax, which serves as a nutrient to the female.

The aedeagus is part of the male's abdomen, which is the most caudal (hindmost) of the three major body sections of an insect. The pair of testes of the insect are connected to the aedeagus through the genital ducts. The aedeagus is part of the male insect's phallus, which also includes in some species the valvae, which are paired organs which help the male hold on to the female during copulation.

During copulation, the aedeagus connects with the ovipore of a female.

In males of most species of Lepidoptera, the aedeagus has a sheath which is supported by an organ called the juxta, which is located between the aforementioned valvae.