Hi Jobele – this can be a sign of disease which occurs in Nature but builds up when you are raising “lots” of butterflies. Disease (whether it is a virus or pathogens etc) has more opportunities to spread when there are multiple organisms (e.g. someone with the ‘flu who goes to school, kindergarten etc).
It might be appropriate to sterilise whatever you are using and in the meantime change the way you are raising your caterpillars etc. Check out the disease hot tag to the right here to see what you can find.
I recently learned about using Milton, found in the baby products section of the supermarket. This won’t affect caterpillars, plants or pupae but will kill any pathogens or virus that is affecting your chrysalises. The formula will no doubt be on the outside of the bottle when you buy it.
Hope this is helpful.
Jacqui