About Therion morio (Fabricius, 1781)
Therion morio (Fabricius, 1781) is a species of parasitic ichneumon wasp that belongs to the family Ichneumonidae. In North America, this wasp parasitizes webworm caterpillars.
Adult T. morio lay their eggs inside webworm caterpillars, piercing the caterpillar's body to do so with their ovipositor. Just like the eggs of H. fulvipes, T. morio eggs have an equatorial disc and a caudal stalk, which gives them an appearance similar to the cartoon oil lamp from Aladdin. Researchers think this shape is an adaptation to help attach the egg to the inside of the caterpillar's integument.
After laying, the egg partially hatches, producing a stage called a "feeding embryo". In this stage, the first instar larva feeds through the inner membrane of the egg that still encloses it. The second instar larva then emerges from this inner membrane and continues feeding on the host caterpillar. The head capsule of the second instar larva is far less chitinized than that of the first instar larva. The third instar larva is similar in appearance to the second; Tothill described it as a "dirty-looking, whitish grub." Unlike the second instar, the third instar larva has spiracles.
