Diet

Conditions and Species of Milkweed

The condition and species of milkweed eaten by larvae can affect its rate of development and adult size. Whilst studying diapause induction, researchers Liz Goehring and Karen Oberhauser found that the butterfly larvae which had fed on older Asclepias syriaca plants developed into larger adults than those that fed on young plants of the same species. Another researcher, Beth Lavoie fed the larvae milkweed fertilized with varying amounts of nitrogen. She found no difference in mass, but rather, slower growth in the larvae which ate plants containing less nitrogen.

Crowding

Uneven Distribution

Although larvae typically occur at low densities in the wild, crowding has been shown to influence the butterfly's larvae development. High density conditions can cause physiological stress, increased competition for food, and an increased susceptibility to pathogens in monarch larvae. Results showed that the butterflies reared at moderate or low larval densities had greater body size, shorter development time, and lower mortality compared to larvae reared at high densities. Exposure to light has interesting effects on monarch development and physiology. Light can even affect the direction that pupae face; the larva in its prepupal "J-shape" and the resulting pupa both face away from the light.