Studies on the behaviour and ecology of Nesciothemis nigeriensis Gambles (Anisoptera: Libellulidae)

Most of the work was carried out at two lakes near to Ahmadu Bello University, Zaria, Nigeria. By the use of painted, dead specimens of this species, other libellulids, a gomphid and models, the species-specific recognition characters have been investigated. It seems that the proportion of dark blue and red on the abdomen and overall size are the most important characters for males. The bright yellow stripe on the dorsum of the thorax of females is probably the most important character enabling males to recognize potential mates. Natural flight movements are not important in recognition of species and sex in N. nigeriensis. By means of mark-recapture of teneral males it has been determined that the normal period of maturation away from water is 12-15 days. The whole of the maturation period of males seems to be spent in the same small area. When sexually immature, male and female are practically identical in colouring and pattern; both having a brownish thorax with a vivid yellow longitudinal stripe on the dorsum and a copper coloured (brownish-orange) abdomen. At maturity, the male is dark blue with abdominal segments 5-9 bright red; the female is brown with a dorsal yellow stripe which is retained from the immature stage. Males live for at least 49 days. Sexually mature males are highly territorial, frequently returning to the same territory day after day, but they are more variable in their choice of roosting sites. The males arrive at their territories late and leave the water early each day, even when the weather is fine. Aggressive territorial behaviour and mating have been seen at the roosting sites. N. nigeriensis is a typical ‘percher’, only flying for about 5 – 6 percent of its time at water. Emergence commences in mid-May and the last imagines are seen in late October in Zaria, their disappearance coinciding with the onset of the harmattan and dry season. It seems likely that the species is univoltine in Zaria. It is only known to occur in the greater Zaria area and in its type locality, Awka, which is 520 km to the south of Zaria. The evidence seems to suggest that it has only recently established itself in the Zaria area.