The female monarch butterfly lays her eggs on the leaves and stems of milkweed plants, such as the swan plant. The swan plant is the main type of milkweed that we have in New Zealand, and this is what monarch caterpillars eat. In America and other places around the world, the caterpillars eat other types of milkweed.
The butterfly places the end of her abdomen on a leaf and pushes out an egg. She sticks the egg to the leaf with a special kind of glue, so it doesn't fall off. She generally lays each egg on the underside of a leaf. She often chooses one of the fresh, new leaves at the top of the plant or end of a branch. This way, when the caterpillar hatches, it has a soft and juicy leaf for its first meal.
In her lifetime, a female monarch butterfly will generally lay 400-700 eggs, mostly one at a time, on different plants. (See more about the butterfly life span here [coming soon].)