That's when the mother lays her eggs. And after days the caterpillar hatches. To survive it has to eat so many plants and leaves. When it's big enough it turns into a larva. Days later it hatches and turns into a ADULT.
It only has 3 stages instead of 4 . So it only egg, nymph, adult . A grasshopper is an example it go from egg then you hatch then and turn in to a nymph and grow up and turn into a ADULT!