Monday, July 20, 2009

What Instar is a Monarch Caterpillar In?

monarch caterpillar larva head capsule remove
monarch butterfly head capsule"I was looking for information on what monarch "instar" stages are? How you tell what stage they are in etc.?"

When a caterpillar outgrows its skin, it crawls out of it, called molting. An 'instar' is the time period between molts. Caterpillar age is usually referred to as 'instars' while people age is referred to in 'years'.

The instar of a caterpillar is determined by measuring the head capsule. The head capsule is on the 'face' of the caterpillar and it never grows. When a caterpillar molts, it removes the old head capsule and has a new larger one in place of it.

1st instar – 0.6mm; 2nd instar – 0.8mm; 3rd instar – 0.9mm (some sources state 1.5mm); 4th instar – 2.2mm; 5th instar – 3.5mm

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