The external factors which release and control prey capture in the praying mantis have been studied in Parastagmatoptera unipunctata and Hierodulae gen. In tests with various kinds of live prey and dummies the strike has been found to be most readily released if I.) the prey is within reach of the forelegs; 2.) the prey moves as a whole while exhibiting rapid, jerky movements of appendages. Size, shape and direction of the prey are less important, while color and odor have no strike releasing value. Continuous presentation of a strike-releaser results in more or less rapid response-waning, depending upon its releasing value. Suboptimal dummies cause complete refractoriness within minutes, while optimal prey continues to elicit strikes after several hours. However, even under optimal internal and external conditions the frequency of strike-discharge declines rapidly at first and then more slowly. By comparing mantids normally raised on live flies with isolated, hand-fed animals and with mantids which were exclusively fed on prey of low stimulus-value, it has been shown that 1.) the strike-releasing qualities of the prey are not learned through experience; 2.) the stimulus-response relations of the subsequent acts of catching and putting to the mouth can be quantitatively modified during the individual life.