One of our hens laid another mystery egg last week. At first glance, the egg looked relatively normal other than being slightly more translucent than usual.

The latest mystery egg.

However, it didn’t feel like a normal egg. See the below picture for how the side of the egg would indent and bounce back in response to pressure.

Mystery egg bending in response to pressure.

What was inside the mystery egg and what was the cause?

It was actually an egg without a developed shell. Instead of a shell, the outside of this egg was just the egg membrane, which is squishy instead of a hard shell.  Inside of the membrane was a normal egg yolk. These shell-less eggs are also called rubber eggs.

Here is a picture of the egg membrane after removing the yolk.

The egg membrane of the shell-less egg.

There are many possible causes of shell-less eggs. One common cause of shell-less eggs is hot weather. We have been having a very warm spell recently so that is a likely cause for this egg.

Other causes of shell-less eggs include a rushed laying when a hen is startled by a predator or a loud noise, calcium deficiency, and age. Hens may lay soft shell or shell-less eggs when they first start laying eggs and when they stop laying eggs during their normal egg laying cycles.

We didn’t eat this egg, but the collective wisdom of the internet seems to indicate that they are indeed safe to eat as if normal eggs. We might try one in the future if we get another one.