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Archive for August 23, 2019

Monarchs Splitting Exoskeleton For The Fifth And Final Time

In the Northeast there appears to be an amazingly large number of Monarch larvae this year, and most of these larvae will complete their metamorphosis by transforming into a beautiful green chrysalis. Once mature, the larva, or caterpillar, wanders about and finds a suitable spot (usually protected and stable) to spend the next two weeks hanging precariously in the wind.  It then spins a silk mat in this location, and puts a silk “button” in the middle of the mat.  It clasps the button with its last set of prolegs (it has three pairs of true legs, and five pairs of so-called prolegs) and spends about 18 hours hanging in a “J,” with its head down, preparing to split its exoskeleton for the last time and reveal the chrysalis within it.

Ba Rea, a Monarch specialist (and publisher of my children’s book, Milkweed Visitors), informs her “Monarchchaser’s Blog” (https://monarchchaser.wordpress.com/about-monarchs/) readers that even though the visible changes between the larval and pupal (chrysalis) stages of a Monarch are sudden, inside the caterpillar these changes are taking place gradually and long before we can see them.  “The parts that will transform the caterpillar into a butterfly are present from the time that the egg hatches.  Inside the caterpillar are “imaginal disks.”  As wonderfully fanciful as the word imaginal sounds, it is actually referring to the adult stage of the monarch which is called the imago.  These disks are the cells that will become the butterfly’s wings, legs, proboscis and antennae, among other things.  By the time the caterpillar is half an inch long its butterfly wings are already developing inside it.

After eight to fifteen days, the adult Monarch emerges from its chrysalis and heads towards Mexico (butterflies that emerge after the middle of August migrate). It is the great grandchildren and great great grandchildren of these migrating monarchs that will return next summer.  (Photo: Monarch hanging in a “J” from Jewelweed, also known as Touch-Me-Not — not the sturdiest of plants to hang from!)

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