Most insects lay eggs, but how this is done, along with the size, shape, and number of eggs laid by different species, is very different.
Egg-laying in insects varies in three different respects. The way they lay the eggs, the number laid, and the shape, size, and pattern of the eggs.
In this article I look at the egg, how insects lay their eggs, the development of the egg, and how insects hatch.
Most insects start their lives as eggs. The larva develops inside the egg before it hatches. Once it hatches, it will eat to grow larger. Larvae do not always look the same in appearance as adults.
Eggs vary greatly in size, shape, and color. Butterflies and moth eggs are diverse, ranging from round to cylindrical barrels. Insect eggs come in almost all colors, and it is not uncommon to see orange, yellow, green, and patterned eggs. Mosquito eggs look like miniature torpedoes, a warning of things to come.
Insect eggs contain an embryo that develops into the larva and enough yolk to consume. Eggs must nourish and protect the embryo until the larva has become fully formed and ready to hatch. Air is supplied through small perforations in the shell.
How insects lay their eggs
Some insects lay their eggs in sheltered areas to protect them, while others will use toxins or have spiky shells. Earwigs will guard their eggs until they hatch.
Eggs can be laid alone, in clusters, or in large groups. The amount depends on the risk of predation that the larvae are likely to encounter. Some beetle species lay a few thousand eggs in large batches, as only some will make it past the larval stage.
Honey bees can lay over 100,000 eggs during their life of two to five years, with an average 1500 eggs per day. The nests have cells where the queen lays her eggs. The hexagonal cells are made of wax. When the larvae hatch, the worker bees feed them from their mouths.
Unlike honey bees, ants, while normally quite regimented lay their eggs in clumps inside the nest, before carrying them to different parts where they are more likely to develop.
Some insects lay eggs by boring through wood, cutting a series of notches into which they lay eggs. Damselflies will lay their eggs inside the stems of aquatic plants, using slits they cut through with ovipositors.
There are also parasitic insects which lay their eggs on the eggs, with some flies laying their eggs on mammals such as horses and cattle. Lice will also stick their eggs to hair or feathers of mammals and birds.
Female insects will lay their eggs where the hatchlings can find food to survive. Many insects will lay their eggs on the same plants that they feed on, laying their eggs on the leaves or the plant’s twigs.
If the plant they feed on is abundant, then the insects will drop their eggs at random, but if the plant is harder to find, they will be more careful when they lay their eggs.
Some insects will only lay their eggs on one plant, but others will drop their eggs on various plants. This choice of plants seems to be from an inherited instinct rather than from memory when they were larvae.
Some insects also lay their eggs underwater. While some underwater eggs hatch out after a couple of minutes of being laid, others need a way to breathe.
Some insect eggs have an air layer built into the egg to allow them to breathe, while others have a small tube built into the egg which reaches the surface. The jelly that you may see on frogspawn protects the egg from drying out if exposed to the air.
Damselflies will lay their eggs by dropping them in the water as they fly across, or by dipping their abdomens into the water to release them.
Some species of flies, aphids, beetles, and cockroaches give birth to live young, after incubating the eggs in the female.
The holly blue butterfly lays two generations of offspring. The spring butterflies, after emerging from pupae, lay their eggs on the holly bush. The second generation of butterflies from late summer lay their eggs on a different plant, ivy. The larva then feeds on the ivy. This happens year after year.
Development of the egg
The egg starts as one cell, but as the nucleus divides into thousands, they form a layer around the outside, keeping the yolk within. The individual nucleeus then forms a membrane around itself to become a cell.
The cells divide into different types of tissues, either forming body tissues or a membrane to surround the embryo and yolk. The yolk provides the nutrients and water to the embryonic cells, while waste diffuses out through the shell.
The cells that form the body tissues are known as the germ band. The band is a flat sheet that then folds on itself. The outer layer becomes the exoskeleton, nervous system, outer digestive tract, and brain, while the layer inside forms the muscles, sex organs, and circulatory system. A third, innermost layer forms the rest of the digestive tract.
Hatching of the insect egg
Larva can either be extremely active before hatching, or show little activity. Some eggs can be seen actually moving around as the larva tries to escape.
Larva can emerge from their egg in a number of ways. They can chew a hole through the egg,
Other species can be seen taking in extra air, or feasting on the yolk to swell and burst their way through. Whichever method it chooses, the larva will then usually feed on the remnants of the egg once it escapes.
Some species will then feed on other eggs, even of their own kind that they can find, although in these species, the female usually only lays one egg in the same place.