What I didn't know was how far this little hobby would go. In Texas I started to find butterfly eggs on the plants about April. As soon as milkweed started to pop out of the ground there were butterflies laying eggs on it. In New York I found Monarch eggs late in the summer. I've found them as late as October too.
The eggs are tough to photograph. They're a pinprick of creamy white. Oval shaped and miniscule. Milkweed bleeds a sticky white substance that will ooze out of the plant if it's scratched or broken. The drops are flat. Eggs are much smaller. But there are aphids and other things on the plants. You'll have to figure it out if you want to raise them. A magnifying glass could help.
When the caterpillars turned into a chrysalis and firmed up (never touch a chrysalis or a freshly hatched butterfly), I'd carefully remove the chrysalis from the roof of the plastic box. Chrysalises attach with webbing and it's easy to gently grasp the stem of a Monarch chrysalis and tug it free. The webbing will come with it.
I'd hook the chrysalises onto the top of a larger cage. I used large safety pins to attach them (through the webbing, handle a chrysalis with extreme care).
It still thrills me to watch a butterfly hatch. There is a general timeline for how long it takes an egg to hatch, the caterpillar to eat a lot of milkweed and grow into a big caterpillar, attach to the roof of a cage/stem of milkweed/bottom of the dining room table when they escape, shed their exoskeleton and form a chrysalis (not a cocoon, that's something else), and eventually become a butterfly. When they hatch it takes time for their wings to expand, they're wet and touching them will ruin them until they've dried and their wings are firm.
When I lived in New York I started tagging my butterflies before releasing them. Monarch Watch through the University of Kansas has an incredible program and sells the tags. We'd carefully log in each butterfly, sex, date, location, and set them free! My family and I learned about the migratory pattern of these amazing butterflies. We learned that they live only a couple weeks and head north in the spring and summer laying eggs. At the end of the season they hatch smaller butterflies that migrate all the way to Mexico (and other places). Those are the ones to catch and tag. They won't be laying eggs. They are on a mission to survive the winter.