Abstract.1A mark–recapture study on the sphecid waspSceliphron assimile(Dahlbohm), analysed by Jolly's stochastic method (1965), was made from 3 December 1974 to 22 February 1975 at Green Bay, St Catherine, Jamaica.2Population levels in an 18.2 ha study area fluctuated about a mean of 281 for males, 259 for total females and 87 for reproducing females, while the probable carrying‐capacity for these reproductives was about 104.3Mean estimated daily survival rates were 0.903 for males, 0.924 for total females and 0.945 for reproducing females. For the first two categories these rates decreased (p<0.02) during the study, probably reflecting increasing emigration. Reproducing females probably do not emigrate and their survival did not significantly decrease.4Minimum age was linearly related to wing wear (r=+0.69,P<0.001) and the latter associated with the progressive maturation and ageing of the ovaries. All surviving females become parous by middle age.5The mean rate of fecundity in the field was dependent on female age and was reduced during prolonged drought. Curves of total achieved fecundity appropriate to realistic survival rates give 4.2–16.8 eggs/female. The Jamaican mean was 9.6 ± 2.3 and that for Green Bay 8.6.6The proportion of females in the Green Bay population was 0.48 ± 0.03 while 0.55 was expected at emergence.7A cyclic budget is used to estimate immigration and emigration, and these were important causes of population change.8For Jamaica, only an estimated 28% of females survived