Candling Eggs

The Secret Life of a Chicken Embryo

Candling is a simple technique, using a light source to backlight the egg, allowing you to see the interior. Work quickly to prevent the eggs from getting too chilled, and in the dark so you can clearly see the changes.

The air sac at the large end of the egg will be evident, getting bigger as the embryo grows.

A healthy egg with a live germ at about ten days of incubation shows as a ‘blush’ sometimes referred to as a spider web, which is the network of veins and arteries.

You can also tell if there is no live embryo by a large dark mass, which moves with the rotation of the egg, or if it’s completely clear.

These eggs must be disposed of in a hot compost to prevent them from becoming explosive under the warm conditions of incubation. Make sure you break the eggs open; if they remain intact they turn into a toxic stink bomb to break open when you spread the compost.

The smell is unbelievable.

At eighteen days of incubation when you candle the eggs a second time you will see that the whole egg will be filled with chick, showing as a solid dark area except for the air sac which will be bigger.

This air sac allows the chick to break out of the shell without drowning in the fluid, so it’s an important part of the process.

Egg shells are porous and allow air exchange as the chick grows, and the enlargement of the air sac reassures you that all is well.

At eighteen days this will be the last time you handle the eggs until after they hatch as turning them (which you will have done three or more times every day) will stop, and you will fill the water reservoirs for the final time.

The incubator will be left unopened and undisturbed until the eggs successfully hatch in two or three more days.

Candling eggs gets easier with practice; the more you do it, the better you’ll get at deciphering the stages of incubation. Read about grafting chicks onto a broody hen and raising chicks for the next stages in increasing your flock of backyard chickens.

For more information on what can go wrong with a hatch, see the Egg Hatching Troubleshooting Guide and find out how to avoid the same problem next time.

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