Size increases after the egg is laid. Larva hatches two days after oviposition by the adult. If not submerged in water, the larva dries out shortly after being dissected. Larvae are located in the host's posterior end. When they emerge from the host, they are much more rugged and immediately begin spinning a tight silky cocoon.
Females bear short ovipositors and parasitize only young larvae or even eggs.
In the laboratory, C. marginiventris lives more than a week, but it is most effective as a parasitoid between two and four days of age. A single egg is usually laid in each host, and the cocoon hatches in seven to10 days. The host, which feeds little throughout its life, dies shortly after the parasitoid emerges. After the mature parasitoid exits the host larvae, they die within a day. The exit hole in the side of the larva is only a superficial sign of the actual damage that occurred to the host.