Most people who have raised monarchs at home or in the classroom know the basics. Monarchs are remarkably resilient and mostly raise themselves if you provide food.
But over the years I've discovered some crucial tips not everyone knows. If you're aware of these tricks, your success can be close to 100%. Roughly in order of importance...
1. Avoid letting milkweed leaves curl. When milkweed dries out, the leaves curl up and trap the caterpillars inside. There's nothing for them to eat or drink. You will have to uncurl each leaf to look for the caterpillars--very time-consuming. Especially, avoid having eggs hatch on dried-up milkweed. If the stem holding eggs is drying out with curling leaves, cut out the eggs on a tiny square of milkweed and transfer each egg to a separate compartment of a white ice cube tray.
2. Spiders are a night-time predator of kitchen or classroom. At night, protect eggs or tiny caterpillars by placing the jar holding a milkweed stem in a saucer of water. Inspect milkweed stems for spiders before putting tiny caterpillars on the plant. Keep caterpillars indoors to prevent parasitism by tachinid flies.
3. Humidity is important for eggs and caterpillars because they live down in the foliage where it's humid--and they don't drink. At all stages, mist them with a plant mister several times a day. For chrysalids, once a day (or not at all) is sufficient. But don't mist too much--let them dry out between mistings to avoid mold.
4. Good quality milkweed food is important. Avoid crusty old plants. By September, milkweed grown in partial shade, or plants that were mowed in mid-summer, make for more tender food. Don't use milkweed grown close to crops, which may have pesticides.
5. You can control the time of emergence of the butterfly (eclosure) to make sure all students see it. When you see the wing colors, black and orange, through the skin of the chrysalid, you know the butterfly will emerge the next morning. When you see the colors, cover the container with a dark cloth. The next morning, the butterfly will emerge within half an hour of your removing the cloth and exposing them to bright light.
6. Avoid letting caterpillars wander when they get large. When small, they never leave the bin if they have good food. But when the size of your little finger, they start to wander and will disappear to form their chrysalid in some hidden spot. At this time, place a porous lid on the bin. If you see a large caterpillar circling on the top edge of the bin, place it back in the bin on milkweed. If it wanders again, put it in an empty bin with a lid of manilla file folders, where it can form the chrysalid.
7. Cannibalism. Probably the biggest danger to monarchs in the classroom is cannibalism. The loss could be 10-25%. In nature, there's usually only one egg per plant. But when we supply eggs, there can be ten on one leaf. Caterpillars normally eat their own eggshell after they hatch. If there's a sibling's egg next door, that may get eaten as well. If you receive leaves with many eggs, you can reduce cannibalism by transferring the tiny caterpillar to a new plant as soon as it hatches. Or you can cut each egg from the leaf, on a tiny square of milkweed, and transfer that square to one compartment of a white ice cube tray. When it hatches, you can easily see it on the white tray.
8. Accidents during emergence of the butterfly. When butterflies first emerge, they are very fragile, and must let their wings dry undisturbed, with enough room to hang and freely pivot about. If they fall down, they will try to climb up but cannot climb on the slick walls of a bin. A butterfly left on the bottom of the bin will become deformed. If you see one fall, you can offer a scrap of paper towel to cling to and lift it up to a place where it can hang, without otherwise touching it. Even better, tape paper towels to the side of your bin, so they can climb up on their own if you are not present. About an hour after eclosure, you can handle a butterfly--but it's best to wait 2-3 hours.
9. Accidents (not disease), are the greatest cause of mortality. Kids are squirrely, but handling monarchs is part of the learning process and should be encouraged. Caterpillars and butterflies are surprisingly robust. Here are the kinds of accidents to watch out for: Dropping a chrysalid on the floor will shatter it. Losing a tiny caterpillar (transfer them over a clear space or white paper). Dropping a caterpillar isn't fatal (but then stepping on it is fatal.) Leaving behind a caterpillar when you switch in fresh food. A butterfly escapes into the room and gets trapped in a window or slammed in a door.
10. Don't confuse a resting caterpillar for a sick one. Each time a caterpillar changes its skin (called molting, happens 4 times), it rests for about 24 hours, sometimes leaving the milkweed plant. It may look sick, but it's fine. It's best not to disturb it, although if you are switching milkweed, you can move it gently. But if it changes color (black), or is inactive much longer, suspect disease or pesticide poisoning. Disease? Quarantine it immediately. Pesticides? It may recover if given food from a different place. When a large caterpillar gets ready to form the J, it spins a silk pad to hang from. Once you see the tiny silk pad under its chin or rear end, it's too late to move it.