Monarch eggs are only about 1.3 cm tall so the baby caterpillar is very tiny. Almost too small to see with the naked eye. I found a pair of eggs on the milkweed in my garden and noticed one had just hatched and the other looked close. I was able to catch the 2nd egg just before the caterpillar emerged from the shell. It will chew an opening near the top of the shell big enough to exit through. When fully out of the shell it will eat what remains for its first meal. Video was captured with a 15x macro lens attached to an iPhone.

Hatching Monarch Caterpillars