Timing:
The very first thing I do when I want to start raising Monarchs each year is check my calendar!
I know I will need a full month from when I bring in an egg to the day I release the butterfly. I will need to have some time every single day of that month to care for my caterpillars. If I have someone who will caterpillar-sit for me if I’m away for a few days, then I just make sure I don’t have more than two or three caterpillars to care for at any given time. I don’t want to overburden someone who is helping me out.
It takes about four days on average from the time an egg is laid until the time it hatches. Of course, unless I see the egg being laid, I can’t be sure how long it has been on a leaf when I find it.
Once the egg hatches, the caterpillar usually takes 14-16 days to grow from the size of the tip of a pen to a few inches long. It needs fresh milkweed leaves every day. Then it climbs to the top of its container for the final time, sits quietly for perhaps half a day, then drops down into a J shape for another twelve hours or so. Finally it shuffles off its skin, revealing the green chrysalis beneath.
At this point I get a break, because once I’ve cleaned the container and readied it for the emerging butterfly all I have to do is check the chrysalis in the morning and evening each day. It just sits there for at least six days, so really that’s just me being a worrier. Somewhere between day 7 and 11 the butterfly will emerge, usually in the morning.
When my butterfly emerges my month of effort is made totally worth it. It is the most joyous miracle, every single time.
Number:
It’s easy to get carried away and bring in all the eggs you can find. If this is your first rodeo, I can not recommend strongly enough that you DO NOT DO THIS:
For one thing, unless you have a field of milkweed (I do.), you will likely end up starving many of them and that will be just awful, for you and for the caterpillars. Expect to need one 4-foot tall milkweed plant for one caterpillar. FOUR 2-foot tall milkweed plants will do, too. Not two 2-foot tall plants! It won’t be enough, because the amount of milkweed doesn’t translate by height in feet. Taller plants have larger leaves.
If you’d like to try raising Monarchs, I recommend bringing in three eggs for your first foray if you have enough milkweed for that many. You may end up with three butterflies, but you will almost certainly end up with at least one and you won’t be overwhelmed by the amount of time and effort it takes to feed and care for them.
I’ve been doing this for close to two decades, I’m very efficient with my feeding and cleaning of containers, and when the caterpillars in the photo above get big it will still take me an hour and a half every day for a week to keep them fed. It would likely take a butterfly newbie four or five hours a day. Do not do this to yourself. Please. It will not turn out well.
Collecting eggs:
Typically it’s the Mama Monarch I see first. She’s fluttering about my milkweed, perching on a leaf here for 15 seconds or so, then fluttering to another leaf to perch for another 15 seconds. I try to keep track of the areas she visits. I’ve seen monarchs lay up to 20 eggs at a time. I plop on my sunhat, grab my egg gathering basket, and go out to gather eggs. It’s Easter in July (or anytime May-September).
This is what a Monarch Egg looks like, right after a female butterfly lays it on a Milkweed plant:
See the little white dot? That’s an egg.
Here’s another: 
Of course, they’re not always so easy to spot.
See this one? 
No? Let me help: 
Sometimes it can be hard to tell the difference between an egg and a bit of white Milkweed sap that has oozed out where a Milkweed Bug (more on them later) may have bitten the plant. Below, the white spot just to the left of the stem is Milkweed sap, and the white spot a bit out to the right of the stem is a Monarch egg:
The key is to check the shape. Milkweed sap will be flat, but Monarch eggs are egg-shaped with a bit of a point on the top. Check out the egg shape here:
Pointy!
I don’t accidentally bring in bits of sap anymore, but I brought in plenty when I was first raising Monarchs. Very disappointing, that. It’s terribly difficult to get sap to hatch.
Caterpillars- to save, or not to save?
Monarch caterpillars in the wild pose a moral dilemma for me. They’re so cuuute! I want to bring them in and care for them and love them and save them all!! I know if I leave them outside the vast majority of them won’t make it.
But. Caterpillars that have hatched in the wild are far less likely to successfully emerge. When I bring in eggs, I have (after years of practice) a nearly 100% success rate releasing them as healthy butterflies. Caterpillars, not so much. *
Caterpillars have often already been infected by Tachinid flies- either directly (the flies lay eggs on their backs), or by ingesting fly eggs on the milkweed they have been eating. Eventually they will explode, all Alien-esque, and leave me with the green goo remains of a chrysalis and some pretty gross squirming maggoty Tachinid fly larvae in my container.
If they’ve escaped the flies, they may have the Black Death. Basically, they turn black, get mushy and die. This has a couple of different causes, one a bacteria and one a virus. Poor caterpillars.
Bringing in eggs leads to more successful butterfly releases for me. But still- the caterpillars. Sigh.
Currently I will bring in caterpillars and keep them in containers on the other side of the room from my eggs. But I only do this if it does not mean I have to leave eggs outside. If I have a full house (I have room for about 35 large caterpillars/chrysalides and 20 eggs/small caterpillars at a time) I will only bring in eggs. Last year I brought in over 80 eggs and still had to leave hundreds to the predators.
I can’t save everyone. I choose to save those who have a better chance at making it. But I sure wish I could save everyone.
∗ I’ve decided I don’t want to put up gross pics here, so if anyone wants a really good look at the revolting diseases and Alien-esque predators that can afflict your caterpillars, I’ve given you descriptions and the proper terminology. You’ll have to rely on Google (or DuckDuckGo!) for the gruesome visuals.