Finding milkweed food can be difficult in September because the plants become "crusty" in late August. By about Sept. 15, many leaves are dying. So, how can you find good food for your caterpillars?
If you cut off the top third of milkweed plants in mid- to late-July, the top will regrow and be much more tender in September.
To find food in September, look for natural areas--like a prairie--that have been mowed sometime during the summer. Milkweed plants there will re-sprout from the roots. These plants will be short and tender. But look carefully, because these small plants may not be obvious.
For example, county roads outside Madison have their shoulders mowed in mid-summer. It's easy to drive along until you spot a big clump of milkweed where the grass is shorter (because it was mowed). Look for an area with houses or woods around, not in the middle of agricultural fields (which probably have pesticide residues). You want to find a plant that is firm, not droopy, and not too old, hard, or crusty. Avoid plants covered with insects like ants, milkweed bugs, or aphids. But if you have to select plants with insects, you can wash them off with a hose.
To collect lots of milkweed, take scissors and a plastic bin. Put empty 32 oz deli containers, or old yogurt containers, in the bottom of the bin. Put an inch or two of water in each container. The large plastic bin keeps the harvested plants upright, while the plastic bin contains any sloshing water.
You could start feeding your caterpillars on another species of milkweed, such as swamp milkweed or butterfly weed. These also die out in September. Usually, I don't recommend these species of milkweed, to keep methods standard, and because the large leaves of common milkweed are easier to work with. However, if you do feed caterpillars with another species, keep in mind that they don't like to change from one species of food to another.
You can extend the life of a cut milkweed plant by placing it in the light, misting it, and cutting off the end of the stem with a sharp knife every few days. Place the stem in water immediately after you harvest it.
If you are short on food, remember that caterpillars will eat milkweed pods, especially if they are not too crusty or dried out.
How to transfer caterpillars to fresh food
Until they are half-grown, caterpillars have to be transferred by hand--using a tiny brush or scrap of paper towel--to new shoots of milkweed. Once caterpillars are half-grown, you can put fresh stalks next to the old ones--the caterpillars will transfer themselves. Neat!
If you are in doubt as to whether a caterpillar is large enough to transfer itself, you can simply cut off the leaf it is on (or a piece of the leaf), and place that leaf on a fresh plant.
Having fresh milkweed is the key to saving time transferring caterpillars--the longer the shoot lasts, the longer you can wait before transferring. So collect fresh shoots just before you need to transfer.
When you discard old milkweed plants, place them in a waste basket without a lid, and don't discard the plants for several days. If you overlooked any caterpillars and left them behind on the old plants, they will climb up to the rim of the waste basket. Check the basket several times. You'd be surprised how many caterpillars you overlooked!
If the food is of decent quality, the caterpillars will never leave it! You don't have to worry about them escaping. One big exception: when the caterpillars are quite large and ready to form the "J," they start to wander, looking for a place to form the chrysalis.
I keep stems of milkweed with their water bottle in a large plastic bin with the lid off--a Hefty Hi-Rise 32 0z. This catches the frass, raises humidity, and reduces touching by kids.
When I see a large caterpillar going 'round and 'round on the rim, I know it is ready to form the "J." To make sure, I put it back on a milkweed. If I see it wandering again, I know positively it's ready for the J.
Now you can either transfer the caterpillar to a mesh cube where it will form the chrysalid. Or, you can keep it in the bin. Make a lid for the bin out of old manilla file folders. Hold the lid in place with tape or small weights. The advantage of a manilla lid is you can cut the chrysalis from the lid with scissors.
Caring for the chrysalis
Requirements for the chrysalis and successful eclosure (emergence):
- Protection: The chrysalis is fragile. It will shatter if you drop it. If a chrysalis is injured but only loses a drop of fluid, it will probably heal.
- High humidity or misting several times a day. Same for the "J."
- A perch: Something to cling to while its wings dry. If the butterfly falls to the bottom of the container right after it ecloses, it will try to climb up to dry its wings. It can't climb the sides of a plastic bin, so you need to tape a paper towel there to provide traction for its claws. If the butterfly remains on the bottom of the container, its wings will be permanently deformed and unable to fly.
- Space: When the butterfly emerges, it needs enough free space to twist around while its wings are drying.
If the crysalis forms inside of a mesh cube on the top, that's a good place, preferred by many teachers. Mesh cubes keep the caterpillar confined while forming a "J," and likewise keep the butterfly contained after eclosure. Disadvantages of mesh cubes are: It's hard for students to see the butterfly emerging. Light is bad, they can't gather around, and the mesh or plastic degrades the view. If you don't disinfect the cubes with bleach, the caterpillars inside could pick up OE spores left by adults from the previous year.
If it forms on an old milkweed stalk or leaf, this is ideal. Simply cut the remaining leaves and branches away, leaving just the one chrysalis on a stalk or branch. Then you can place the stem in a jar to hold it upright. I like to display chrysalids on a stalk because it's natural, while students can gather on either side to watch the butterfly emerge.
What to do with chrysalis that attaches to the wrong place and has to be moved? There are several techniques. If it attaches to a plastic bin, you can tease off the silk pad with a pin, or shave it off with a craft razor. Roll your fingers over the lifted pad to make a ball of silk. Then use a pin or small alligator clip (from a hardware store) to attach it to something like a branch. Or, you can take a piece of dental floss and tie it around the cremaster (the stalk of the chrysalis). Once the floss is tied, pull the chrysalis off and then tie or pin the floss to a stick or mesh cube where you want the butterfly to emerge. It's a good idea to pin a label with the date of formation next to each chrysalis, so you know when it will emerge.
When setting up a display of emerging butterflies, where they can be seen in the open, don't worry about them escaping right away. They won't fly for at least 2-3 hours, probably longer, while their wings are hardening. If you have to handle them during this time, get them to crawl onto a q-tip. Avoid touching their wings.
A newly emerged butterfly isn't hungry until hours later, probably not until the following morning. Then you can feed it a honey solution (1 part honey to 9 parts water) using a q-tip. Butterflies can taste sugar with their front legs; usually they will extend their proboscis (tongue) when the legs touch the q-tip.
If this doesn't work after multiple tries, you can gently extend their tongue using a pin. Point the pin at right angles to the plane of the rolled-up proboscis, then move the pin tip into the roll, and pull sideways to extend the proboscis. Touch the extended tongue with the q-tip. One hand holds the butterfly's folded wings, the other holds the pin, while a third person touches the extended tongue with the q-tip. In all delicate work like this, it helps to brace your hands (or wrists) on a solid object like a table.
If a butterfly does escape into the classroom, don't panic. Close the doors and windows. They are attracted to lights. Turn off the lights, so they won't get entangled there. The butterfly will then probably fly to the window. It may not be able to get a grip there, so it will slide down to where you can reach it. You can hold the open mesh cube to it, hoping it will fly in. Or better, simply clasp the wings together with your thumb and forefinger. If the butterfly remains out of reach, wait till night-time, when it will be inactive and may leave the window.