The following observations are presented:- 1) A description of male: female interaction in A. aquaticus and A. meridianus. This indicates the presence of a male discrimination mechanism in that large females are selected for the passive phase before their smaller counterparts. 2) Passive phase durations in allopatric and sympatric populations of A. aquaticus and A. meridianus. No significant difference was found between species; however two populations of A. meridianus differed significantly from each other (<0.05P). The duration of passive phase is shown to be substantial (means varying from 5.3-11.2 days). Intermittent pairing was shown to occur, in particular with small females. 3) The relationships between the parameters a) female size: day the passive phase commenced for each couple and b) female size: day each female became ovigerous. That is large females were found paired and became ovigerous before their smaller counterparts. Both relationships are shown to be significant (at 0.05 level of probability or less) in four of the five populations investigated. It is suggested these observations may be interpreted in the following way: Males of both species are selecting for passive phase association those females exhibiting a cue which correlates with imminent oviposition and large brood size. This cue may be female size or another characteristic which is correlated to size. This behaviour pattern yields an increase in offspring number to those males exhibiting it.