The Monarch Butterfly

Perhaps no butterfly in the U.S. is as well-known as the Monarch (Danaus pelxippus), a member of the Nymphalidae or brush-foot family. The adult butterfly only appears to have 4 legs as the last 2 insect legs are very small and are located near the butterfly's head. As adults, these butterflies are clever mimics utilizing Mullarian mimicry to reinforce the warning colors and distasteful qualities of several related species, gaining all three species more protection from predators.

The Monarch butterfly (Danaus plexippus) starts life as a tiny white egg, ovoid in shape and deposited singly on the leaves and flowers of milkweed. The diminutive larvae develops inside the egg and eventually eats its way through the eggshell, quickly making its first home into its first meal.

Monarch caterpillars go through 5 instars or periods of growth between molting when the caterpillar will shed its skin. At each instar the caterpillar is usually at a particular range of size  and has certain characteristics. Newly-hatched caterpillars are barely visible, and their green coloration is designed to blend in with the leaves they are eating.

As it grows larger, the caterpillar develops the distinctive white, yellow, and black stripes many people recognize. This striped pattern seems very obvious, but it actually helps hide the caterpillars from predator eyes by breaking up their shape and making them harder to spot.



These changes in size and coloring allow us to figure out where they are in their development process and then know about how much they will need to eat. Monarch larvae are prolific eaters and can strip milkweed plants bare with remarkable speed.  Rearing monarchs can be a real challenge for this reason and also because they are susceptible to several diseases and many predators.

Once the Monarch larvae has reached its full size it will attach itself in a protected  place using a tiny pad of silk spun from organs called spinnerets.

Over the next 24 hours or so, the larvae will slowly shed its skin revealing a green pupa beneath which is called a chrysalis. (See a video here.) The chrysalis of the Monarch is a pale  green and feels waxy to the touch. Tiny spots and lines of iridescent gold mark the surface of the chrysalis making it a truly beautiful sight to behold.

As the butterfly inside undergoes metamorphosis, the chrysalis skin begins to thin and become clear, revealing the developing butterfly inside. After about two weeks, the fully formed Monarch ecloses from the chrysalis and will be ready to fly in a few short hours.

The adult Monarch can live up to about a month and spends that time searching for a mate, feeding, or possibly ovipositing (laying eggs). The male Monarch can be distinguished from the female of the species by a raised black spot on the lower wing. This raised area is a pouch on the wing that produces scented scales called androconia that males use to help attract females.

Male (top), Female (bottom)

Monarchs in peninsular Florida are non-migratory and have an established year-round population in the Tampa Bay area. (Learn more about Florida's pocket populations here.) But in the central U.S., the monarch is one of the best-known migratory creatures of the animal kingdom with individuals travelling up to 3,000 miles so that they may overwinter in highlands of Mexico. This core population is currently suffering severe challenges after an 80% drop in population in recent years. Learn more about migratory monarchs here.