The castors and oil sacs from beavers can be valuable to the trapper either to sell or to use for making lure. Castors and oil sacs are not very difficult to remove from a beaver if you know where the castor is located and how to remove them without rupturing or cutting them.
1. First, you need a beaver, as shown below. The castors and oil sacs are located just above the vent. Note there is no external evidence of the sex of this beaver.
2. Make a cut from the vent up the belly just under the fur about eight inches. If you are skinning the beaver for fur, you may want to wait until you're done skinning the beaver to remove the castors and oil sacs. Cut shown below.
3. Peel back the fur on each side of the cut to expose the area where the castors and oil sacs are located. The castor and oil glands are hidden under a thin membrane of muscle - the reddish pink membrane is clearly visible in picture #3.
4. Carefully cut through the membrane and begin peeling it away from the castors. The castors are right below this membrane, so care must be taken not to cut the castors. I find that if I pinch the membrane between my index finger and thumb, I'm able to pull the membrane away from the castor and safely cut through the membrane.
5. Once the membrane is cut away and pulled back, you can see the castors on each side. Below the castors you can see those two pink looking tubular shaped glands. These are the oil sacs. Also, on this beaver you can easily see it's a male. At the upper part between the castors, you can see the beaver's penis. A female will only have a thin membrane at this location.
6. Next I gently grasp one castor with the fingers on one hand and with the fingers of my other hand I pull the membrane off of the castor and work it out. The castors need to have all the red membrane removed from them. The castors can be very delicate and can tear easily if too much pressure is applied. Different castors can take different amounts of pulling before tearing. The best way to get a good at this is by doing.
7. After working both castors free of the membrane, two cuts need to be made to free it from the beaver. The first cut is from the penis as is shown below where the knife blade is located. Its the same on the female, except there is only a thin membrane to cut.
8. The location of the last cut to free the castor is shown below where the knife blade is. This cut is made where the castors are attached to the vent. The oil glands can be easily seen above where this cut is to be made.
9. On the tail of the beaver is the set of castors that were removed. They are nice and full and will be partially dried and ground in preparation for using them in making lure. Notice that there is none of the pink membrane on the castors. It's important to make sure it is all removed.
10. To remove the oil glands, simply cut the mebrane around them., then cut where they join at the vent. I like to cut them so they remain with membrane keeping them attached to one another. It is not necessary to remove the red membrane from the oil sacs if they are to be milked of their oil.
11. On the tail of the beaver is shown the set of castors and the oil glands.
12. After I have the castors and oil sacs removed, I like to hang them on the lip of a 5 gallon bucket that I keep in my truck. This begins the drying process for the castors and oil sacs. I like to dry both the castors and oil sacs until the outside gets a leathery feel to it. In low humidity it takes about four or five days. I will then place the partially dried castors in a freezer until I have accumulated enough to make a good batch when ground. I find that the oil is easier to milk from the oil glands after they have dried that four or five days.