The pupal stage is an important one: while pupae do not require much direct care, they can have very specific demands which vary a lot depending on the species of butterfly/moth and their biology.
While a pupa may seem like a simple waiting game, there is much more to be considered. Temperature for example; some butterflies and moths from temperate regions overwinter as pupae. For overwintering, they will require a period of cold temperatures. If stored too warm they will outright refuse to emerge and die instead. The cold period of winter is a biological requirement for these pupae to emerge. This may be induced by storing them in your basement or refrigerator.
On the contrary, tropical species would most probably die or fail to emerge if stored in a cold environment, and require constant warmth and humidity to properly emerge. Their biology does not take cold into consideration, as most tropical areas have no pronounced seasons and are constantly very warm and humid.
Some species may not rely on temperature at all. African species for example will generally wait for a rainy season instead of a typical summer or winter. Their emergence may be triggered with a sudden increase in humidity after a period of drought.
As you can see, the needs of a pupa to emerge differ greatly per species, mostly depending on their origin and general biology. Temperature, humidity.. even light intensity and length plays a role in some species. It is greatly recommended to research the natural life cycle of a species when taking care of their pupae, and trying to recreate the conditions from their natural habitat.
Important is to store pupae in a slightly humid environment as pupae are very vulnerable to desiccation. They are unable to “absorb” moisture but a humid environment will prevent them from drying up. This applies to every species in general.
Up next, if you’ve done everything right is emergence, my favorite moment! Briefly after emerging butterflies and moths will have tiny, shriveled wings. The first thing it will do is climb or hang and find a secure spot to inflate the wings. Gravity aids them during this process, which is why they need to hang against a wall or in some cases upside-down. Some species have hanging pupae and they require to emerge “upside-down”: after emergence they will hang on to their empty pupal casing which provides them grip and a safe place to hang while pumping the wings. Many moths do the same and hang on to their cocoons. For example:Argema mittrei (male) rests on the cocoon after eclosing
Generally pupae will emerge just fine when placed on the floor of a butterfly cage placed on a towel. Although there are exceptions, mainly Nymphalidae which require to hang upside down during emergence. The pupae can be suspended with a needle or glue.
While fairly straightforward, there are a few things to consider when dealing with pupating larvae. First of all, there are many different ways a caterpillar can pupate. Some spin a cocoon, some burrow themselves and pupate in a subterranean chamber, some spin a girdle and other larvae will pupate hanging upside down while attached to a silk pad. (Mainly Nymphalidae) Important is not to disturb or stress pupating larvae, this may result in failure and death. Subterranean pupators can be offered ar substrate in which they can burrow – like soil or paper towel.
It is very important to study the conditions your species needs – and then trying to recreate them.Caterpillar of Acherontia atropos burrows to pupate – in some bird nest material (strings and cotton)
Prepupal caterpillars decrease in size because in this stage they evaporate all their excess water. But most Sphingidae and Saturniidae pupate in a cocoon or underground, where there will not be too much evaporation since there is not much ventilation because they pupate in a small and well isolated spot. Now if you leave them out in the open in your house, they will dry out and die because of excess ventilation and airflow , taking out too much water in the process. Spraying does not help much because prepupal larvae do not absorb water. The key is airflow and humidity!! They need good substrate that does not expose them to open air and that absorbs the excess humidity (too wet is also not good). Spraying can help moisten the substrate and maintain relative humidity but the larvae do not need to be wet. Paper towel or garden soil works. Letting them pupate in airtight plastic boxes helps too.
Butterflies can pupate in the open air since they are used to this. They will attach themselves to a surface with silk and pupate.
I have always had great succes overwintering pupae outside, in the Netherlands. In the Netherlands, winters are reasonbly mild and soft, and most palearctic and temperate Asian species will survive them. This is also guaranteed to work with any species that are native to your country, since (obviously) they will be able to handle the winters native to their habitat. By isolating the pupae with towel or other substrate (moss, leaf litter) they can be sheltered from the harshest of frost. Overwintering box
What I prefer to do is to place the pupae and cocoons in a well isolated, airtight plastic box, and cover them with towels (actual towels) and also paper towel. This box can be placed in your shed, or in a well-covered shaded area outside (in a bush). Butterfly and moth pupae are a also very populair snack for several kinds of small rodents that will struggle to obtain food in winter (such as mice or rats) – make sure rodents are unable to get into the overwintering box, or they will raid it without mercy!
Species that overwinter from “softer” climates, such as Arizona, Texas or Mexico, can be overwintered cool but frost free spaces such as basements. Species from such areas will require a colder winter, but cannot tolerate harsh frost, since they will freeze to death.
It is also possible to overwinter species in a fridge, but this is much riskier than overwintering them outside. Fridges have a strong dessicating effect on livestock!
Here a useful video:
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