I wanted to put together a post of odd eggs that we have gotten over the years.  To understand why mishaps occur in the egg laying process, though, you should first know how normal eggs are laid.

If you have a rooster in your flock, chances are most or all of your hens will lay fertilized eggs (eggs that will produce chicks if properly incubated).  Each egg takes 24-36 hours to form.  After the yolk is released from the ovary it travels through the oviduct.  It is fertilized in the Infundibulum, the albumen (or the egg white) is added in the Magnum, the shell membrane is added in the Isthmus, the shell is added in the Uterus or Shell Gland, and the bloom is added in the Vagina.  Most of this is self-explanatory, but many people have never heard of the egg’s bloom.  This is a clear coating the egg is covered with to seal the pores so bacteria cannot enter the shell.  Air, however, can still go through the pores.  (This is why you can wipe off eggs to be incubated but you should never wash them.)

No Shell

Here’s an egg with only the inner membrane and no shell (also called a rubber egg).  Hens can lay eggs like these at the beginning or end of their laying cycle or if they get scared (usually at night as a result of predators or stormy weather).  You may see these eggs occasionally in your flock.  If your hen lays eggs like this regularly, it may indicate a lack of calcium, phosphorus or salt in the hen’s diet; or an abnormality in the shell gland.

These eggs are normal in every other aspect and can be eated, but are usually torn open by the chicken (or the farmer).  If left out too long they will start to dry out.

No Yolk 

Sometimes a hen will lay a tiny egg (here are 3 that I’ve emptied and saved).

These eggs usually have no yolks are often called wind (or fart) eggs, dwarf eggs or rooster eggs.  Many times an egg without a yolk is one of the hen’s first eggs, laid before her system is working properly.  These eggs also occur when a piece of tissue breaks away from the hen’s reproductive tract and is treated like a yolk as it travels through the oviduct.  When this is the case, a small piece of greyish tissue can usually be seen in the albumen.

Egg with a “Tail”

This egg was such a surprise.  The shell was hard like a normal shell everywhere, except “tail” and where the “tail” met the egg.  That part of the shell wasn’t hard but it wasn’t quite as soft as the membrane of the shell-less egg above, though.  It is thought to be caused by the egg not being hardened enough before being laid.  The soft part of the shell is then elongated as the egg is being passed.

Double Yolk Eggs

Double-yolk eggs occur when 2 yolks are released at the same time, or when they are released close enough together that they become encased in the same membrane and shell.  These eggs can occur at the beginning of a hen’s laying cycle, but some hens are genetically predisposed to lay double yolk eggs on a regular basis.  (It’s similar to fraternal twins running in families.)  In hens that lay these eggs only occasionally, the egg laying cycle is usually interrupted.   Hens generally lay an egg every 24-36 hours but if they skip a day, the next egg that they lay can be a double-yolk egg.  These eggs rarely hatch 2 chicks if incubated.  Multiple factors are at play: each yolk may not be fertilised and if they both are, both chicks may not survive pipping without careful assistance.  Below is a double-yolk duck egg: