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Guest Post: Marion Leahy

18 March 2022

We love hearing from our members. Marion Leahy wrote to us recently about raising monarchs. This is what she shared with us:

I began studying the monarch butterfly life cycle long before the advent of the Trust. Over the years I have observed:

The egg hatches!


This begins white and changes to grey as it develops. When the little black spot, the head, appears it is ready to hatch. It will eat some of the egg case for the first meal and possibly a small ring of the soft layer on the leaf before going up to the new leaves.

The five instars... they grow in size about 3,000 times!


The caterpillar will outgrow its skin and to do so they often move to a dry stick or down the plant stem where they anchor themselves in order to crawl out of their old skin. They will stay in this position for some time, secured by silk. This prevents them being blown or washed off. At this stage they should not be moved.

They grow steadily as they eat, and need to change to another skin four times.  The larger caterpillars change quicker. When they are fully grown and ready to change into a chrysalis (fifth instar) they will be large, fat and so firm that a gentle hold does not impress upon the body.

If the leaves should run out caterpillars will eat the stems of young plants which will dry out the plant and it will die. A tight clip can save the plant. Meanwhile they will also eat the flowers and seed pods.

Pumpkin and cucumber should never be fed to caterpillars. Alternative foods such as cucurbits will often lead to deformed butterflies - but also, we are not sure what it is doing to the parts we cannot see, such as reproduction, migration, diet of the next generation. 

When food has run out I have found that left alone caterpillars will go to hang by themselves, even half and quarter-sized ones. These will become perfectly formed miniature males and females.

The 'J' or prepupa

The 'J' form or prepupa

When the caterpillar is ready to hang it will choose a spot and it will extend and wave its body around. This is so to ensure that there is enough room for the wings to expand when it leaves its chrysalis. It will create the white knob that it will hang from. When this is ready it will turn around and attach its rear end onto the knob.

The 'J' will hang while the innards become semi-liquid but every drop is a specific part of the butterfly. As the time passes, the yellow rings take on a greenish tinge. When this is complete the 'J' will straighten out. Shortly after, it will ‘pulse’ from the top to split the skin over the head. If the caterpillar skin divides further up the 'J', or the change goes too slowly, the skin will dry out and not move. It is very quick to concertina the old caterpillar skin upwards, then to wriggle and shake it off. The chrysalis will then tighten up to the lovely shape with the gold dots we know.

Newly formed chrysalis


Starting as a misshapen light green sac, they quickly tighten up. At this stage the new case is very soft and is easily damaged so should not be touched. When it is hardened, a fallen chrysalis can be re-hung by its webbing, or if it has no webbing it can still hook onto a piece of re-used webbing, but you have one chance to do it as the hooks are very delicate. A chrysalis lying down will still eclose as long as it is cradled against something it can climb up, as it has to be able to hang the wings freely.

The shade of green gradually darkens and as it does the formation of the wings can be seen. When the chrysalis goes dark it is first a greyish black but it goes a clear, shiny black when it is ready to eclose. This is because the butterfly separates from the transparent cuticle. Again, the cuticle divides at the face of the butterfly, and the legs and proboscis appear. When the feet have hooked onto the fine ring around the old case the body is flipped out backwards and the wings freed. The body is full of fluid, meconium, which the butterfly uses to pump into the wings to extend them fully. They will stay hanging until all wings are down, then the fluid is expelled from the body. They will not move until the wings are dry and stiff, but then they will wish to fly soon after.

Should a butterfly fall from the chrysalis it must be lifted immediately for it to survive. It should be lifted by holding your finger under its feet and moving it onto somewhere safe. Should it not hold on and you persevere it will frantically try to get up but not stop moving. The fact that the wing stage has been interrupted I have found that they end up with the equivalent of brain damage. Although the butterfly may end up looking okay, it does not fly properly but flops around the ground.

DCF 1.0

How many legs can you see? But insects have SIX legs!

Points to Ponder...

Have you noticed that the butterflies only use four of their six legs as legs? The front two legs aren’t used for standing – they are vestigial and now used for signalling or communication, and testing the quality of the leaves.

For years a little boy, now a grown ship master, used to come to my place visiting with his grandfather. His first question was always 'Are there any caterpillars in their sleeping bags?'  The little skin on the floor was likened then to the pyjamas left on the floor, just as children do.

I know you will know most of this from your own observations,  but I thought it would be a help to others if the sequences were noted more clearly, as there is a lot of mis-information around.

Thank you for the glossary on the website.

Regards, Marion.

P.S. There is an excellent site for information, that of the Monarch Joint Venture.


2 comments on “Guest Post: Marion Leahy”

  1. I have copied & pasted this into my documents, as it very clearly sums up the life cycle for those who are interested.

    Thank you Marion Leahy, & thanks to MBNZT for printing it

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