Overwintering Techniques > Refrigerator
Nevertheless, using the refrigerator can be an effective overwintering technique if butterfly immatures are exposed to the right amount of humidity and provided with airflow. Your strategy in caring for immatures wintered in the refrigerator follows the following immature groups based upon sensitivity:
1. Pupae and Mature Last Instar Larvae. Keep in container with screen top. Mist spray every 14 days or so during the front end of winter; every 7 days or so on the back end. Adjust according to how immatures respond to humidity in their natural habitat. This group of immatures are LEAST sensitive to dessication and mold.
2.   Caterpillars that overwinter as half-grown larvae such as many brushfoot butterflies, some sulphurs, some satyrids, etc. need more care than pupae and mature last instar larvae. They require mist spraying at least every four days; but not so much that creates mold. Some trial and error is needed to fine tune your own strategy. Overwintering these immatures outside in a protected terrarium might be more advisable.
3.   Butterfly eggs, larvae that overwinter as unfed first instar, or Limenitis hibernacula: This group is the most sensitive to desiccation on the one hand or mold on the other. If you overwinter any immatures of some Speyeria, Boloria, Cercyonis, etc, you need to pay very close to them.
Here is a container with butterfly immatures in the refrigerator. The humidity in this container is great; but there needs to be enough airflow in this container (by having a lid with a large enough hole where this humidity can dry up) so that it will dry up. Otherwise, mold can kill immatures. Photo courtesy Abe Homan.