Monarch Butterfly Chatbook – Classic J Shape


When a caterpillar hangs in a classic J shape, it is ready to change into the pupa  (PYOO-puh) stage. I actually saw this poise. One day I was visiting a pond in the village and saw beautiful swamp milkweed (Asclepias incarnata) growing near a pond’s edge. This was the only time I noticed monarch caterpillars eating milkweed flowers; they  had already eaten all the leaves on the milkweed plants. I visited the site for a few days. It wasn’t long before the caterpillars were no longer seen on milkweed plants. They may have found shelter on another plant or twig to begin the next stage of their life cycle.

Watching caterpillars in the wild is interesting. One day after a summer rain, I witnessed a caterpillar hiding under a milkweed leaf. The caterpillar was upside down with the abdomen prolegs clinging to a milkweed leaf. The caterpillar was peacefully fast asleep. Milkweed leaves can be large and this may help a caterpillar stay dry or hide from predators at night. Don’t be surprised if caterpillars go missing in late afternoon. They usually return to the top of milkweed leaves in the daytime once the sun warms them up by mid morning. 

In the fifth and last instar stage when a caterpillar is ready to shed its final skin it will no longer eat between the larva and adult butterfly stage. The caterpillar has an average of two or three weeks to complete its journey as a larva.

It is amazing to watch a caterpillar shed its last skin and change into a pupa or sac. The whole transformation takes place within a matter of minutes. Once the pupa is formed it is soft and needs to harden in order to protect what is within.