Egg

Scanning Electron Microscope (SEM) Image of Egg

Monarchs usually lay a single egg on a milkweed plant, often on the bottom of a leaf near the top of the plant. The eggs hatch about four days after they are laid. While butterflies and moths do not care for their young after the eggs are laid, female monarchs do lay their eggs on an appropriate food source for the larva. They secrete a small amount of glue to attach the eggs directly to the plant. Female monarch butterflies lay an average of about 700 eggs over two to five weeks of egg laying, with a record in captivity of 1179!

Each egg is surrounded by a hard outer shell, called the chorion, to protect the developing larva. The shell is lined with a layer of wax, which helps keep the egg from drying out. The eggs have tiny funnel-shaped openings at one end, called micropyles. These holes penetrate all the way through the shell allowing sperm to enter since eggs form their hard shell prior to fertilization. The raised areas on an egg shell are called ridges. They are formed before the egg is laid.