Egg-citing Eggs: Educator Resource

What Are Eggs?

Eggs are amazing structures that serve as the starting point for many animals' lives. They come in various shapes, sizes and colors, and are designed to protect the developing baby inside. Eggs have a shell on the outside, which can be hard or soft, and on the inside, there is the yolk and egg white that nourish the growing animal.

Animals That Lay Eggs

Many different animals lay eggs. Some of the most well-known egg layers are birds, such as chickens, emus, and ducks. Reptiles, like turtles, snakes and lizards also lay eggs. Amphibians, including frogs and salamanders, and even some mammals, like the platypus and echidna, lay eggs too. Insects, like butterflies and ants, and fish, such as salmon and goldfish, also reproduce by laying eggs. Gastropods (snails, seasnails, slugs, squid and octopus) also lay eggs. So, in short, chickens aren’t the only ones!

Where Eggs Are Found

Eggs can be found in a variety of places, depending on the animal that lays them. Birds often lay their eggs in nests made from twigs, leaves and feathers, which they build in trees, bushes or even on the ground. Some bird nests are intricate woven structures (like the satin bower bird), and others are just a ‘scrape’ in the sand made by rubbing their chest feathers back and forth (looking at you hooded plovers!).

Reptiles might bury their eggs in the sand or soil to keep them safe and warm. Amphibians usually lay their eggs in water, attaching them to plants or floating freely. Insects often hide their eggs on leaves, in the soil or in other protected areas. Fish lay their eggs in water, sometimes creating nests in gravel or attaching them to underwater plants.

Some parents are more attentive to their eggs than others. Some parents, like sea turtles, follow the ‘set and forget’ method of parenting, where they lay their eggs in a safe place and leave them to hatch by themselves. Other parents are very attentive! A mother platypus will seal herself inside her den with her eggs. The eggs hatch after around ten days, but she will stay in the burrow, nursing them with milk for three to four months.

Egg Characteristics

The size and colour of eggs can vary greatly. Bird eggs, for example, can be as small as a pea, like those of a hummingbird, or as large as a grapefruit, like those of an ostrich. Egg colours can range from white and beige to blue, green and speckled, helping them blend into their surroundings and avoid predators. Once we leave the kingdom of birds, eggs get even more interesting!

The Port Jackson shark has an amazing screw-shaped egg case. When she lays an egg, she uses her mouth to wedge it into a rock crevice and ‘screw’ it into place. The egg case then hardens, locking it into place. Other sharks, like dogfish, lay eggs called a ‘mermaid’s purse’ with long dangling streamers at either end that tangle in the seaweed and help camouflage the eggs.

Shark egg cases aren’t the only eggs you might find on the beach. Have you ever found a jellybean-shaped clear blob on the beach? Or a curved collar shape that looks like it is made of sand? You’re looking at seasnail eggs! You might also find squid or cuttlefish eggs. These look like a mass of long, white, squishy fingers joined together in the middle. If you hold them up to the light, you can sometimes see the tiny creatures growing inside. If you find these eggs on the beach you might want to return them to the water to give them a chance of surviving.

Egg Development

Inside an egg, a baby animal, called an embryo, grows and develops. The egg provides all the nutrients and protection the embryo needs until it is ready to hatch. This process can take anywhere from a few days to several months, depending on the species. They provide a safe and nutrient-rich environment for the next generation to develop. Some small birds, like the Hummingbird or the Silver-eye, can take as little as ten days to hatch. The longest incubation periods for birds are around 80 days and are found in some species of albatross, kiwis and megapodes (brush turkeys, mallee fowl, etc).

Flies have some of the fastest-hatching eggs outside of birds and can hatch in as little as 24 hours. A species of octopus (Graneledone Boreopacifica) holds the record for the longest time eggs are guarded, and a mother can brood her eggs for up to four and a half years. That is one dedicated parent!

Eggs-citing Eggs: Whose Egg?

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