When eating crabs, one of the most delicious foods on Earth, you might notice some slimy substances when cracking open the outer shell.
If you boil crabs without cleaning them, you will encounter most of the innards still intact when you remove the outer carapace. While there are certain parts of the crab guts that you should not necessarily eat (such as the lungs), other parts are OK to eat.
One such substance is the “yellow stuff” or “orange stuff” encountered when opening the shell. Contrary to popular belief, it is not crab poop even though it looks like it!
Yellow Stuff – “Crab Mustard”

The yellow colored substance found inside a cooked crab is known as the hepatopancreas, and is an organ responsible for filtering impurities from the crab’s blood.
Some people consider this a tasty and delicious part of eating crabs. It is not necessarily bad for you to eat it and often times it adds a nice flavor.
When pulling your food directly out of the ocean, there is always a small chance that the crab could be infected in some way, however boiling at high temperatures should eliminate some of the risk.
Orange Stuff – Crab Roe (Eggs)

Sometimes when you open a female crab shell (which are identifiable by their “red painted nails”), you will find orange crab roe inside. This is not the same as the “mustard” which can also be seen in the picture above. Think of it more like a caviar.
When crabbing, you should consider throwing females back, especially if they have the large egg sac protruding from their carapace.
When cooked properly, this is OK to eat.

In conclusion, the yellow stuff is OK to eat and some people find it very tasty! Crab meat may also be a good way to lose some weight.