Wednesday, 24 January 2018

Metamorphosing into chrysalides 

A Tailed Emperor Charaxes sempronius Caterpillar curls up in preparation for metamorphosing into a chrysalis - the final stage before it then metamorphoses into an adult butterfly. (See the previous posts for further details on my watch of these caterpillars)

I counted seven caterpillars on the host food plant, a Persian Silk Tree, and as I watching them over the days, I noticed that the first had disappeared a few days ago. So I traced the branches, looking for any wanderers. I first found one crawling swiftly along a branch, heading away from the leaves where it had grown, and probably where its egg had been laid. I measured its pace and was surprised that it was travelling at 20 m per hour. Not bad for a 6 cm long caterpillar. This is probably the most vulnerable stage in its life as it was exposed, with no camouflage while on the bare branches and predatory birds could easily spot it if I could. I found three, and one was still feeding, so where were the other three. Had they found a secluded spot or had they been eaten?

Once they had selected a suitable spot to settle, they fixed themselves by the a specialised hooked organ, called a cremaster at their tail end, to a silk pad they prepare on a branch. Then they hung down on it, and kept wriggling in a curled position to begin with.

Hours later, they let themselves go and hung down straight. This is when they begin to metamorphose.

However - all three of the ones I could find changed into their chrysalides overnight. I set up a slow-motion camera on two of them, but that only worked in daylight. By morning the chrysalides were almost fully formed. The shot above was taken late in the evening. The shot below, of the same animal, was taken next morning. The leaves of the tree close up at night and open by day.

The chrysalis forms inside the old skin of the caterpillar, and when ready, it breaks through the back of the skin. The old skin is then wriggled up to the tail end where it dries and is shaken off. All is complete. I shall now wait about two weeks and try to capture the emergence of one of the butterflies from a chrysalis in slow-motion time-lapse.

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