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. In Florida, it is abundant throughout the summer, but its populations decline from October to April. At 25 degrees C it develops in 13 days from egg to adult. Hosts C. marginiventris is a general parasitoid of noctuid moths. A single egg is usually laid in each host, and the cocoon hatches in seven to10 days.