contrary to modern forms, the female roachids all have a well-developed external ovipositor, a primitive insect trait. they probably inserted eggs singly into soil or crevices. the egg pods, called ootheca, seen in modern cockroaches and their relatives is a new shared trait separating them from their primitive ancestors. some of the roachid species could reach relatively large sizes compared to most of their modern relatives, like the carboniferous "archimylacris" and the permian "apthoroblattina", the latter who could reach 50 mm in body length. however, none that we know of reached near the size of today's largest tropical species, the modern 'giant cockroaches', such as the famous hissing cockroach.