There are four stages to the life cycle of a butterfly and it will take them a month to go into the larvae. In the meantime get some pest control to get rid of them.
Swallowtail caterpillars will become pupa when the weather is cooler, often in fall. Depending on your location, this may be approximately one more month. They will emerge around April as beautiful butterflies.
It really depends on how much they eat. Depending on the type of plant. It might make sense for you to do a google search or go to a local shop. I am sure you can find the answer.
