Vlindertjes.eu

The egg or ovum

This is the stage where a lepidopterans life begins. An egg is actually a large cell and consists mainly of nutrients for the development of the embryo. Around the nutrients a membrane (vitelline membrane) is present and a hard shell which is called chorion (eggshell), this combination protects the contents of the egg against fungi, bacteria, dehydration and mechanical stress. The chorion contains microscopic holes that are called (aerophyle), these aerophyle ensure the exchange of oxygen and carbon dioxide which the embryo uses and releases during its development. One single and larger opening to the outside world is the microphyle, this opening is important for the fertilization of the egg and allows the sperm cells to pass through to fertilize the egg. Of course the ovum also contains a cell nucleus with a single set of chromosomes.

By fusion of a single set of chromosomes of the male lepidopteran and a single set of the female lepidopteran, a nucleus with an unique set of chromosomes is formed. Unlike mammals for example, it’s not the complete cell that will start to divide but only the cell nucleus, these nuclei nestle against the inside of the vitelline membrane and form the blastoderm. After forming the blastoderm, cells will locally continue splitting to form a thicker line with cells, in this thickened line, cells will start to specify and at the end develop into the caterpillar. Some of the unspecified embryonic cells will stay dormant, these dormant cells are activated by hormones during the pupa stage and will eventually grow out to a butterfly or moth.

A fully developed caterpillar, works its way out through the eggshell with his jaws. Some species have fault in their eggshell so that the young caterpillar can escape by applying pressure from inside the egg. The development of the young caterpillar inside the egg usually takes 7 till 20 days, in many cases it’s the overwintering stage and it will take many months before the caterpillar crawls out of its egg.

Appearance

Lepidopteran eggs can vary tremendously between species, in size from a couple of hundredths of an inch to eggs with a diameter of nearly a quarter of an inch. The shape of the eggs may also vary considerably, from sphere, hemisphere, oval to a closed donut shape and cone-shaped to urn shape and each can have their own structure. Smooth, grooves or pits come in many sizes and patterns and what the colour is concerned, there are many possibilities. Almost all eggs are surrounded by an adhesive which is often transparent but also can have a tan, this adhesive glues the lepidopteran egg to the surface it’s laid on. Most eggs will change colour one or two days before hatching, because the almost fully developed larva gives the contents of the egg a different colour. In some cases the eggshell is transparent and the fully developed larva can be seen through the eggshell. The picture at the bottom of the page shows a transparent egg, the larvae can be seen clearly through the eggshell.

Deposition

Eggs can be deposited in many ways, individually, grouped or as single package, groups and packages in various patterns. Usually they are deposited on leaves of the host plant. Overwintering eggs will most often be laid on branches or on the trunk of a tree due to leaf fall during autumn. The brown eggs of the Oak Eggar (Lasiocampa Quercus) have a nearly perfect sphere shape and no adhesive, they are just dropped during flight over heaths. That is possible because the larvae that hatch are surrounded by their host plants. The Gypsy moth (Lymantria dispar) female deposits her eggs as one large package on any solid surface near the place where she emerged and covers the package with hair from her abdomen. As the young larvae emerge, they spin a thin silk thread and let themselves be carried away by the wind, they will nearly eat any food plant they land on. The Lackey moth (Malacosoma Neustria) glues her eggs in a spiral around the twigs of its host plant in the shape of a cylindrical sleeve so it’s impossible to fall off. The Map butterfly stacks her eggs in one egg wide, 10 - 20 eggs high pillars under the underside of leaves and so do all species have their own way of depositing their ova. Many just hatched caterpillars consume a part, or all of their eggshell as a nutritious first meal.