Reproductive behaviour of Onychargia atrocyana was investigated from tandem formation to post-ovipositional resting. No male territoriality, aggression or courtship display was observed at the mating site. The species preferred to mate and oviposit on Alternanthera philoxeroides stems or Colocasia esculenta petioles. The duration of copulation was 212–568 sec. Copulation was accomplished in three stages involving abdominal flexions and wing flapping. The female oviposited while in tandem on submerged stems and petioles of macrophytes. Oviposition was endophytic in rows forming a zigzag pattern. There were distinct post-copulatory (8–92 sec.) and post-ovipositional resting phases (up to 225 sec.).