Each butterfly 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.
Each egg has one to many tiny funnel-shaped openings at one end, called micropyles. Since eggs get their hard shell before they are fertilized, this hole, which penetrates all the way through the shell, allows sperm to enter.
The raised areas on an egg shell are called ridges. They are formed inside the female before she lays the egg. Butterfly and moth eggs vary greatly in shape.