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Black Swallowtail (Papilio polyxenes) Butterfly Farming Entomology Monarch (Danaus plexippus)

What is a Butterfly Caterpillar “Instar”?

An “instar” refers to the developmental stage of insects that undergo incomplete metamorphosis, such as butterflies, between molts. Insects have exoskeletons (hard outer coverings) that do not grow or stretch as the insect inside does. As the insect grows, it becomes too large for its exoskeleton. To accommodate this growth, the insect must shed or molt its old exoskeleton and produce a new, larger one.

Black Swallowtail caterpillar.

For butterfly caterpillars, the period between hatching from an egg and pupating into a chrysalis involves several molts. Each growth stage between these molts is called an instar. Typically, butterfly caterpillars go through five instar stages, but this can vary depending on the species.

With each successive instar, caterpillars usually have a noticeably different appearance, often growing in size and sometimes changing in color or pattern. The process from one instar to the next involves the following steps:

1. The caterpillar eats and grows until it becomes too large for its current skin.

2. The caterpillar stops eating and finds a safe spot to begin the molting process.

3. The old exoskeleton splits, and the caterpillar wriggles out, revealing a new, softer exoskeleton underneath.

4. The new exoskeleton hardens and becomes more protective.

5. The caterpillar resumes eating and growing until it reaches the next molting point.

After the final instar stage, the caterpillar will seek a suitable location to pupate and form a chrysalis, transitioning to the next phase of its life cycle. With each instar representing yet another miracle, observing and learning about butterflies becomes a miraculous experience… one day at a time!

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