According to the movements of the 6 abdomen, the copulation process in I. asiatica is divided into 3 stages (I, II and III). The mean duration of each stage was 75.8 ± 8.8 min, 6.4 ± 0.3 min and 15.8 ± 0.9 min for stage I, II and III, respectively (S.E.). No sperm transfer was found during stage I. The prolonged duration in stage 1 was related to the time of onset of copulation. Sperm was transferred into the bursa copulatrix during stage II. Although stage III was a phase without apparent abdominal movement, the sperm transfer was continued, following the sperm migration from the bursa copulatrix to the spermatheca. Immediately after copulation termination, the estimated number of sperm was 64,500 ± 4,425 in the bursa copulatrix and 43,143 ± 6,397 in the spermatheca (S.E.). The role of each stage in copulation will be discussed from the viewpoint of sperm competition.