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Rearing Monarchs



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Monarch Rearing Kit

Your Monarch Rearing Kit (available here) contains 14-16 first to third instar monarch larvae (caterpillars) that were started on an artificial diet. Upon arrival, these larvae should be transferred to larger containers and provided with milkweed leaves. Monarch larvae will feed on all commonly available milkweed species (but do not confuse these with other plant species with a milky sap). Milkweed plants can be collected in the field (cut stems) and stored in a refrigerator in plastic bags for 4-5 days. Leaves should be rinsed and dried before feeding. Do not feed the larvae leaves that are yellow, dried out, or moldy. If the milkweed plant has not been in your care, leaves should be washed in warm, soapy water, rinsed well, and dried before feeding. This will help prevent illness and death of the caterpillars due to pesticides. (Please note: Plants that have been sprayed repeatedly or sprayed heavily may contain residual pesticide that will harm the larvae, even with washing.)

Rearing Containers
Monarch larvae can be reared in many different types of containers, such as aquaria, glass jars, plastic food containers, etc. Rearing containers should be at least three inches deep and should have ventilated lids (use either mesh lids or poke holes in the lid). Larvae will survive best and attain a large size if you keep the food fresh, the container clean, and the humidity and crowding low. Controlling humidity is very important. If the humidity is too low your leaves will dry out and will not be a good food source; if the humidity is so high that condensation forms in the container, mold may develop on the frass (feces) and/or the leaves. These conditions seem to favor the development of diseases that could spread rapidly from larva to larva. Your larvae will do best if only a small number are reared in each container. To minimize the possibility of cross-contaminating containers, DO NOT transfer larvae from one container to another. Should a larva die of an apparent disease, for example lose its shape and color, transfer the healthy larvae to a clean container with new leaves and clean the container with the dead larva with hot soapy water or bleach. You can find examples of rearing containers and cages here.

An easy rearing method, which requires less daily care, is to place the larvae on milkweed whose cut stems are placed in water in narrow necked bottles – 2-liter plastic bottles work great. First, cut the milkweed stems twice under warm water; this will keep the milkweed fresh. This treatment has the effect of keeping the latex that typically forms on a cut stem from plugging the vesicles that transport water to the leaves. To keep larvae from going down the stems and drowning in the water, wrap the stems with a paper towel so that it fits snugly into the neck of the bottle. The bottles can then be placed in screened cages. A variation on placing the bottles in a cage is to construct a container of two plastic 2-liter bottles. This rearing container is made by 1) cutting the bottom off of one of the bottles, 2) drilling/cutting a 3/4 inch hole in each of the bottle caps and gluing them together (top to top) with a strong adhesive. Fill the bottom bottle with water, screw on the caps, attach the other bottle and add the plant stem. The top opening can be covered with screen or any other porous cover - we use a small square of open-mesh shelf liner. Four to six larvae can complete their development in this container. The plants should be changed as needed, usually every two to three days. Photos and more detailed construction directions are available here.

To rear monarchs outdoors on living plants outdoors you will need to protect the larvae from numerous parasites and predators. Protection can be provided by using mesh "sleeves" with draw-strings on either end. The sleeve is placed over a plant, the larvae placed inside, and the drawstrings tied tightly. This method works well and little care is involved.

Rearing Conditions
The larvae you’ve received should be transferred to a rearing container with milkweed as soon after their arrival as possible. To transfer the larvae, open the cups and use a fine paintbrush, toothpick or forceps to gently transfer the larvae to a suitable rearing container. Alternatively, you can add leaves to your rearing containers and place the open cups inside. The larvae will then crawl from the cups to the leaves. Line the bottoms of the containers with paper towels. Add 2-3 leaves to each container and provide new leaves and a new paper towel every day or as needed. Once the larvae have reached the last (5th) instar stage (approximately 1" in length), they will feed rapidly and can quickly run out of food. Watch the containers closely at this stage; you may have to feed the larvae twice a day. Development times of larvae depend on the temperatures at which they are reared. At room temperature, the larvae should pupate 10-14 days after you receive them. Generally speaking, lower temperatures translate into longer development times and higher temperatures decrease development time.

Pupation and Emergence
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.

Emergence Cages
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.

Adult Feeding and Maintenance
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.

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