As soon as the cement on the lips of the ootheca is broken, all nymphs wriggle out, molting their embryonic skins as they do so. If one or two fail to emerge when the others do, they perish, as they are not able to force the ootheca open again. The whitish, newly-emerged nymphs begin to run around actively in about 10 minutes. The first few molts of the nymph occur at approximately monthly intervals, but thereafter may vary from one to six months. The duration of the nymphal period from records now available varies from 285 to 616 days, with an average of 409, although the final average will be over 450 days.
Growth is slower during the winter months, although maturity is reached any month in the year.
The average development period of six male nymphs was 426 days and that of 11 females was 396 days. He also found that body weight approximately doubles between molts and the cockroaches may reach sexual maturity in seven months under optimum conditions. In the laboratory, approximately 24 weeks are required from egg to adult at 80 degrees F. and R.H. of 50 percent. The wing pads become evident in the third or fourth instar. The sexes in the early instar are distinguished by the fact the female has a sharp medial notch in the caudal margin of the ninth sternum which is either lacking or very slightly indented in the male.