Chrysalis (or pupa) size within the same species of butterfly or moth will often vary.
The adult butterfly’s size is determined by the size of the chrysalis. The chrysalis size is determined by the size of the caterpillar when it pupates.
What are the factors that determine size? There are three basic factors that determine the size of an adult butterfly.
The Queen Alexandra Birdwing is the largest butterfly in the world with wings up to a foot from wing tip to wing tip. In the US, the Giant Swallowtail measures up to 6 1/4 inches from wing tip to wing tip.
2. Sex of the insect. In some species, males are larger. With other species, females are larger. In the remaining species, males and females are basically the same size.
Black Swallowtail females are generally larger than males.
Monarch males are generally larger than females.
The amount of food the caterpillar eats determines its size when it is ready to pupate.
~ Runs out of food (must pupate early, before time)
~ Runs out of food (spends energy running between plants)
~ Taste of food (contaminated by sprays or other items on the plant)
~ Taste or texture of food (end of plants’ life or season, tough leaves, old nasty leaves)
~ Taste of food (less favorable species of host plant)
~ Competition for food (too many caterpillars, not enough food)