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How to Overwinter a Chrysalis

Black Swallowtail in chrysalis stage of life cycle
Spicebush Swallowtail Butterfly Chrysalis
Spicebush Swallowtail Butterfly Chrysalis

As the cool weather of fall approaches, it only takes a few simple preparations to overwinter a chrysalis as it enters diapause. Following nature’s lead and adding a little safety from predators will give your chrysalises their best chance for survival through the winter months.


What is Diapause?

Diapause is basically the insect’s version of hibernation. Butterflies can enter diapause in all four stages of the butterfly lifecycle. However, each butterfly species uses one particular stage (two in a few species) to enter diapause and survive the winter.

Amazingly, in preparation for diapause, the egg, caterpillar (larva), chrysalis (pupa), or adult butterfly actually starts producing a form of internal antifreeze to prevent damage from freezing weather during the winter. Some of the butterfly species that overwinter as a chrysalis (pupa) include but are not limited to the Swallowtails. Others are the Checkered White, Mustard White, Orange Sulphur, Clouded Sulphur, Elfins, and some Skippers.

Diapause is triggered mainly by shorter day length and temperature. However, there is a large range in the time-frame that a chrysalis will go into diapause. In other words, you may have some chrysalises entering diapause in August while others don’t until October. In the fall I often have Black Swallowtails from the same group doing two separate things; some fly off and others overwinter as a chrysalis. The butterflies that emerge are released while the other chrysalises are soon placed outside as the temperatures start to drop.


Needs of an Overwintering Chrysalis

Green form of a Black Swallowtail Butterfly Chrysalis
Green Form of a Black Swallowtail Butterfly Chrysalis

For a chrysalis/butterfly to survive the winter it will need to be exposed to cool/cold weather and short day lengths (no artificial light on a regular basis) to keep it in diapause. A butterfly that emerges from a diapaused chrysalis will not be able to survive the cold winter weather like other butterfly species that overwinter as adults can.

An overwintering chrysalis needs ventilation but also exposure to some humidity to keep it from drying out. The natural humidity of the winter air will be enough for a chrysalis but our dry indoor air may dry a chrysalis (even in an unheated section of your house) unless some additional moisture is provided (like misting). On the other hand, if the chrysalis is tightly closed up in a consistent high humidity/wet container, mold can occur which would be detrimental.

An overwintering chrysalis needs protection from predators. A chrysalis makes a yummy winter treat to a mouse, bird, or other critter. Parasitic wasps and ants can also cause a chrysalis fatality in the fall and spring if they are a problem in your area.


Overwinter a Chrysalis Outdoors

If a butterfly is native in your area, then the chrysalis will generally have no problem surviving a normal winter. Because the chrysalis needs short days and cold temperatures to keep it in diapause, probably one of the best places you can keep it is outside in a protected area. In nature, a caterpillar will form its chrysalis in a sheltered area on a structure or on some branches/stems in a planted area. The number one advantage you can give your chrysalis over a chrysalis in the wild is protection from predators.

A container holding a chrysalis should be vented on at least one side with some form of screen or netting to keep mice, birds, and other critters away from the chrysalis. Place your container in an area out of the sun so the chrysalis does not get too warm on a sunny day. Shelter the container from direct rain/snow especially if it is a type that could flood or fill with water. Although a chrysalis can withstand exposure to rain and snow, it does not need it to keep from drying out. The humid winter air will provide enough moisture. Screened porches, covered porches, sheds, unheated garages, or a location under protective overhangs will work great as a place to keep your overwintering container.

Once your chrysalis is in a protected container/area then there is not much more you need to do to overwinter the chrysalis except check on it from time to time and wait for the miracles of spring!

Brown Black Swallowtail butterfly chrysalis
Brown form of a Black Swallowtail Butterfly Chrysalis


Overwinter a Chrysalis in the Refrigerator

I have never tried this so my information here comes from research rather than experience. In researching this topic there appears to be a large difference of opinion. Some people swear by it and have used it exclusively for years while others have described bad experiences. In my personal opinion from reading what all I could find on this topic, it is probably better to use nature (outdoors/garages/sheds etc.) instead of a refrigerator as long as that is an option around your home.

The biggest problem with the refrigerator method is the uncertainty about the amount of humidity the chrysalis needs and the differences in refrigerator performance. Some refrigerators have drier conditions than others. A lack of humidity will kill a chrysalis by drying it out while too much humidity will cause molding which is deadly to the chrysalis.

As a result of the differences in refrigerators, there is quite a difference in procedures. Some recommend using an airtight plastic container with no misting all winter. Others recommend (probably the majority) using a container that allows airflow and misting the chrysalises every 7-14 days.

If you experiment a little, you could certainly find a procedure that works in your refrigerator and that may turn out to be your ideal solution for chrysalis overwintering. I may have to give this a try sometime. When I do, I certainly will share my experiences!


The end of Diapause

The primary triggers that start diapause (day length and temperature) also marks the end of diapause for overwintering chrysalises. Knowing when to bring your chrysalises out of a shed or garage is always a little tricky. You may want to bring your chrysalises in the house to watch them eclose. There are several factors you can use to judge this. First of all, be aware that your butterfly will probably not emerge any sooner than two weeks after you bring it into warmth and daylight if it has not already started coming out of diapause.

Some advice for timing this is to bring the chrysalises out of diapause when the trees start leafing out. Another way to judge is to watch for other butterflies showing up in nature that also overwinter as a chrysalis. You can also make a judgment on the availability of nectar plants in flower. All combined, you will probably find that your butterfly is ready to come out around April to May depending on where you live.

underside of a green black swallowtail butterfly chrysalis
Underside View of a Black Swallowtail Butterfly Chrysalis


A Few More Comments about Chrysalis Overwintering

  • Most homes are too warm and dry for overwintering chrysalises. In the past I learned this by keeping Black Swallowtail chrysalises in the house and ended up with about 25% of them emerging too early in the spring. I misted them occasionally so they did not dry out but the house just wasn’t cool enough to reliably keep them all in diapause.
  • Some chrysalises will actually stay in diapause well into the summer and some have reported even up to 18 months! Don’t give up on your chrysalises unless they have obvious defects (dry and “crunchy”, holes, splits, etc).

If you have any questions or information about how to overwinter a chrysalis, I would love to hear from you so please feel free to Contact me. Good luck with your overwintering chrysalises!