The life cycle of cockroaches begins with the egg. Cockroach eggs hatch because of the combined pressure of the hatchlings within. Upon emerging from the egg case, or ootheca, this immature form of cockroach is known as a nymph or baby cockroach. Nymphs are bright white in color initially. They enlarge through the intake of air and will harden and darken within hours. Recent experiments have also shown that the availability of food within the first 12 hours of molting greatly affects the growth of cockroach nymphs.
Cockroach nymphs are grayish-brown in color and darken with each progressive molt. The nymphal development to adult ranges in length from months to over a year. Cockroach nymphs are similar to their adult counterparts. Cockroach nymphs undergo a series of molts. They emerge as full adults from their final molt.
German cockroach nymphs are often less than 3 millimeters long when they hatch. After darkening, they are almost uniformly dark, with one light patch located on the back. This patch becomes more pronounced through the second and third molting stages. Brown-banded cockroach nymphs have two bands on their bodies which range in color from black to light gold. American cockroach nymphs are gray-brown in color and gradually redden.