Casualties happening late in the Monarch Butterfly season are unfortunate, yet will always happen as the season cools down.
Butterflies/caterpillars/chrysalis rely on warm weather temperatures to be well and active. When temperatures cool they face diapause, as their bodies basically begin to slow down into an almost state of suspension.
"In animal dormancy, diapause is the delay in development in response to regular and recurring periods of adverse environmental conditions. It is a physiological state with very specific initiating and inhibiting conditions." Wikipedia
Knowing how our season was winding down and temperatures rapidly cooling, I brought a number of 5th instar Monarch caterpillars into our house to stay safe while finishing their caterpillar processes, forming their chrysalis and then flying off to their butterfly life.
It's warmer in the house, so I thought they would have a better chance of survival - and I could keep an eye on them.
Right now I have 18 chrysalis, 2 caterpillar J's and one final caterpillar still growing.
Unfortunately, as each day grows colder there have been casualties, even in the house.
I believe the problem stems from the caterpillars beginning a semi-diapause process and don't have enough strength or energy to complete their processes as they would in warmer temperatures.
Main problems seem to be -
1) They are taking longer to reach their best 5th instar size in order to set into a J.
2) They are taking longer from the time of stopping eating and making their silk button.
3) They are taking longer from the time of making their silk button, to hanging into their J.
4) They are taking longer from the time of forming their J to forming their chrysalis.
5) They are taking longer in the chrysalis before emerging as a butterfly.
Today, sadly, one caterpillar didn't make it from J to chrysalis and died part-way through the process.
Then another J, that did make it through to chrysalis stage, had made such an ineffective button that it had no grip and the chrysalis fell near the end of the process. The chrysalis was too damaged to keep, so I have euthanised it by putting it into the freezer. In the freezer they just quietly close down, go to sleep, and then freeze to death.
On a positive note, where there are casualties there are still many positives with successful butterflies emerging.
Click along each picture, below, to see a closer view.......