Our new method saves time, is more natural, and requires less equipment.
The old method
During 2019, we recommended raising small caterpillars in a shoebox sized plastic container or a 32 oz deli container, both with a mesh vent in the lid. Inside, you'd place one tiny caterpillar on a single milkweed leaf, with the leaf getting water from a floral tube. When the leaf dried out in a few days, you'd have to transfer the caterpillar to a fresh milkweed leaf. We recommended 1 caterpillar per container, to reduce transmission of disease between caterpillars.
The new method
Use a cut stem of milkweed with 4-6 leaves, instead of single leaves. Place the stem in water in a salsa jar about 4 in. high, with a hole in the lid for the stem. (Make the hole by hammering a screwdriver into the metal lid.) Use two stems in two jars, with about 5 caterpillars per stem. As the caterpillars grow, you can use larger and/or more sprigs, in more jars. When the caterpillars are about half grown, they will even transfer themselves to the fresh stems, if you arrange them so new stems touch the old stems. Place the jars in a large plastic bin. Mist the milkweed food in the bin several times a day.
When providing fresh food, always check the old milkweeds carefully for overlooked caterpillars before you discard them in a wastepaper can. Keep the can for two days before you permanently discard the old stems; if any caterpillars remained undetected in the old stems, they will climb to the top of the wastepaper can where you can find them.
Cover the bin at night, mainly to prevent entry of spiders which might eat small caterpillars. During the day you do not need a lid for the bin, because caterpillars never wander if they have good food. Except they do wander to form the chrysalis. So, when you see the first large caterpillar leave the bin, that means they are about the form the J and it's time to put a lid on the bin.
Why I recommend the new method
- You don't need to purchase small containers or floral tubes. The mesh vents in the small container are time-consuming to make.
- It's less work to feed the caterpillars. It's a lot of work to transfer small caterpillars to fresh food. Since the stems remain fresh longer than single leaves, you have fewer transfers, with less chance of losing or injuring small caterpillars.
- There's less mess and disease. The floral tubes often leaked inside the small containers, mixing with frass, making a mess and increasing the risk of disease. With the new method, the frass stays dry. You can simply shake frass out of the bin when you refresh the food.
- With less risk of disease, you can raise more caterpillars in a smaller space, with a higher % of success.
- When you raise caterpillars on stems in an open bin, this allows the humidity to cycle up and down, similar to the natural environment. Mist the stems and bin several times a day, then let the bin dry out. The tiny mist droplets allow the caterpillars to drink if they need to, while the dry periods kill mold which might otherwise form.
- It's easier for kids to see the caterpillars and their social behavior. If your kids are old enough, you can even take the jars out of the bin and place them on a table (with paper under the jars to catch the frass).
- For the large container, I recommend a 32 qt Hefty Hi-Rise bin available from Walmart, with plastic screening or an old manilla file folder taped over the top to prevent escape at night. Some people use aquariums or a "Critter Keeper." (Critter Keepers are both fragile and expensive.)
Preventing disease
Using this new method, I've had almost no disease, despite raising hundreds of caterpillars together. I screen the egg-laying females for OE disease. If you keep the caterpillars indoors, that probably eliminates the small tachinid flies that parasitize caterpillars. If you soak used equipment in 10% bleach and wash the milkweed food under cold running water (and inspect for spiders), that will do the rest. Remember, don't allow a container (like a mesh cube) that has held butterflies to come into contact with caterpillars without sterilizing it first. If any of your butterflies emerge infected with the OE parasite, they will be covered with OE spores that can later infect caterpillars.
Equipment for raising caterpillars
We sell the underlined equipment (at our cost):
- Mesh cubes, $7.00. 1 foot on a side, black mesh, with vinyl window one side, and zipper access. Folds flat. Very useful for observing butterflies emerging from chrysalid, or for holding butterflies to feed or move them prior to release. Not recommended for holding caterpillars. When you put butterflies in or out, face the zipper opening away from the light.
- Kritter Keepers, used. $10. Many people use these to raise caterpillars. They are OK for this, except that they are fragile and overpriced. We recommend Hefty Hi-Rise containers, below. But these used Kritter Keepers are priced right!
- Hefty Hi-Rise plastic bin with lid, 32 qt size. Used for raising caterpillars. When the caterpillars are as large as your little finger and starting to wander, you need to cover the container with thin cardboard (a manilla file folder works) or plastic screening. The caterpillar will attach its chrysalid on the cardboard--you can then cut out a small square with the chrysalid and attach it to a bare branch for holding and display of its emergence. Available for ~$9 from Walmart; you can order it on the internet and have it shipped to your home.
- Watercolor brush, finest. Used for transferring freshly hatched caterpillars from a leaf or ice cube tray to fresh food. You can also use the corner of a small piece of ripped paper towel.
- Ice cube tray, white. Used for hatching eggs. Cut individual eggs off the leaf, on a piece of leaf about 1/16-1/8" square and put one egg in each compartment of the tray. Place the tray on top of a wine glass, with the bottom of the glass in a saucer of water. When the eggs hatch the tiny caterpillars are easily seen and removed with the brush, then placed on fresh food. The wine glass prevents them from escaping. The saucer keeps spiders from eating the eggs at night. From Target or Dollar Tree.
- Magnifying glass, about 10x. Used, with a pocket flashlight, for seeing if eggs are about to hatch (have black tops), or for checking if the egg is really a monarch egg.
- Flashlight. Good lighting is essential when working with small objects like eggs. This small flashlight is bright and inexpensive. Two for $10. Batteries not included.
- Black plastic garbage bag. Used for placing over a container with chrysalids, to exclude light. When chrysalids first turn dark, cover them in the afternoon so as to exclude all light. The next morning, butterflies will emerge from the chrysalis within half an hour of removing the cover.
Transferring caterpillars to fresh stems of milkweed
If they are resting (inactive, not feeding) between molts, it's best not to disturb them. During this time you can easily transfer them by cutting out a small piece of milkweed they are resting on, then placing that piece on the new food.
More coming...
Be careful not to rub your eyes when handling milkweed.