The reproductive behaviour of the damselfly Disparocypha biedermanni (Chlorocyphidae) was studied in various streams, mainly in the Lake Poso area of Sulawesi. Flight styles of males were analysed in detail for the first time using high speed cinematography. Protracted threatening flights were particularly common between territorial neighbours. Males flew with regular counter-stroking wing beats and the abdomen held horizontally. Occasionally one of the males performed short ascending flights, pausing the wing beat. These threatening flights were interrupted periodically by short bursts of increased intensity with higher stroke frequency where males arched their abdomens. The escalated threat display could be intensified by tremulous horizontal changes in position. Unlike most Chlorocyphidae, mating took place without courtship and oviposition was in vertical mossy structures well above the water. The female was guarded by the male only at the start of oviposition. Possibly the mating system evolved in such a way as to avoid interspecific competition with other Chlorocyphidae but this needs more supporting evidence.