When the larvae have finished growing, they will spin a small silk button, or pad, at the top or side of their container. The larvae will hang upside down from this pad and will assume the J-shaped position of the prepupa. Do not disturb the monarchs when they are preparing to molt to the pupal, or chrysalis, stage.
The pupae usually form in morning hours (9-11 am) or later in the day (5-7 pm). You will notice the larva expanding until its skin splits to reveal a green cuticle. This cuticle hardens and the larva will become a pupa, also called a chrysalis. If the pupae are kept at room temperature, the butterflies should emerge from the chrysalis within 10-14 days. Again, cooler temperatures will delay emergence and warmer temperatures will shorten the amount of development time required.
An emerging monarch will cling to its pupal case. At first, the butterflies are soft and their wings wrinkled and pliable. Their abdomens will be large and you may notice the abdomen pulsating as fluid is pumped from it into the wings, until the wings are fully expanded and become stiff.
It usually takes 1-2 hours for a monarch's wings to harden sufficiently for flight. The new adults are relatively inactive and do not need to be fed the first day. During the first 24 hours the wings will harden and the sensory mechanisms (eyes, odor receptors on the antennae, and taste receptors on the ends of the leg - yes, butterflies taste with their feet!) will become fully functional.
You may want to consider moving your pupae from rearing containers into emergence chambers. This will ensure each butterfly has enough room to dry and expand its wings and will help prevent the spread of disease. The pupae can be moved after they have hardened, about 48 hours after pupation, by gently pulling up the silk pad with forceps.
Once they have emerged, the monarchs can be released or can be used for classroom instruction, student projects, or to start a breeding population in the classroom.
When the adult butterfly emerges, it must be able to hang with its wings downward to facilitate their expansion. Therefore, pupae must either be hung vertically or placed near a rough vertical surface to climb onto.
Picnic food protectors (available from some drug and discount stores) make good emergence cages. A pizza box with a rough surface (screen, washcloth, etc) on the bottom can be used for a base.
The pupae can be hung (attach tape to the silk strands at the end of the pupa or tie dental floss around the cremaster - the end of the pupa that attaches to the silk) inside the food protector or placed flat on the bottom of the box.
If the pupae are hung by the cremaster, the new butterflies will cling to the pupal case as in the wild. If placed on a rough surface, the new butterflies will crawl across the bottom and climb up the walls of the food protector to expand and dry their wings.
Individual emergence cages can be constructed by gluing window screen inside a 12 oz or larger clear plastic cup. The butterfly will use the screen to climb up on when it emerges from its chrysalis. The edge of the screen should extend to the bottom of the cup and the cup should be placed over the pupa on a paper towel or other rough surface.
The newly emerged adults will not need to be fed the first day, but the next day they can be fed a sugar-water or honey-water solution.
Mix 1 part sugar or honey with 9 parts water and pour into a shallow dish. A plastic pot scrubber should be placed in the dish to aid in feeding. The food must be changed every day to prevent fermentation.
As an alternative, you can buy an artificial nectar mix from Monarch Watch. This artificial nectar will not ferment; therefore, you only need to top it off every 2-3 days.
If you have a large cage, the butterflies can learn to self-feed; the feeding solution should be placed near the top of the cage and relatively close (within 20 inches) to the light source. Like most insects, monarchs will fly toward lighted windows or artificial lights.
The butterflies will live for 2-3 weeks if they are well fed, but they may live as long as 6 weeks if the temperatures are cool enough and you take good care of them.