Gypsy Moth Life Cycle
By Jacquie Bede
Dept. of Plant Science, McGill University
Here is how the life of the gypsy moth unfolds through the seasons. In the fall, females lay their eggs, normally in crevices in trees. She covers the eggs with a layer of setae (hair-like structures) that help to keep the eggs warm and also deter any predators. The eggs go into a phase called diapause; essentially, they wait out the winter to hatch as larvae (caterpillars) in the spring. Male caterpillars typically have five larval instars (caterpillar sizes) compared to the females that have six instars. I can only imagine that females need the extra stage to take in more nutrients for the eggs that she will eventually lay. The caterpillar stage is the gypsy moth’s most destructive phase because they feed on the leaves of trees (mainly) and cause defoliation.
After the caterpillar stage, the insect will make a pupa. In the pupae phase, a complete tissue rearrangement prepares the adult to emerge as a moth. The adult male moth is smaller than the female moth. His brown wings features an interesting pattern. In contrast, the female gypsy moth is white with brown ripples. The most confusing fact about gypsy moths (at least for me) is that while both the male and the female have wings and can theoretically fly, adult females of subspecies Lymantria dispar dispar cannot fly whereas adult females of subspecies Lymantria dispar asiatica can. I remember being once told that the adult female Lymantria dispar dispar is laden with so many eggs that she only has limited, if any, flight. The good news is that there is only one gypsy moth generation per year.
Gypsy moth life cycle illustrated:
