Geslachtsbepaling / What sex is my skink

Blue tongue skinks are notoriously hard to sex.

Probing has been proven inconclusive, as the "pocket" being probed is not different enough in length between the sexes the way it is, for example, with snakes.

Popping hemipenes is a method that can be very accurate if you know what you are doing. Unless you are highly experienced in the method, you should absolutely not attempt it. You'd be subjecting your skink to risks of severe injuries, possibly leading to broken spines, damaged/prolapsed hemipenes requiring amputation, and the death of your animal, and after all that subjected risk, unless you were successful in popping out the hemipenes, you'd still be left uncertain as to whether you truly have a female or just weren't able to get the hemipenes out.

Popping veins is another method some very experienced keepers have reported success with. It is similar to popping hemipenes, but instead of popping the entire hemipenes out, they look for a prominent vein that can also be popped in males. This method is also very accurate when you know what you are doing and what you are looking for, and carries slightly less risk for hemipene muscle damage, but is still risky if you are not highly experienced in it.

Some of the less risky methods of sexing:
Behavior sexing. This has been described on the general Caresheet. It can be highly risky as well if you end up putting two males together; it is possible to go from two skinks seemingly avoiding each other to a bloodbath in a split second. Broken spines and torn-off limbs have been reported. Whenever you introduce ANY two skinks together, whether you know their sexes or are trying to figure it out, you must remain within reach of them at all times and be ready to intervene.
Can it be accurate? Yes, if you know what you are looking for. It is not risk-free, and it actually is not conclusive. We've had many members reporting skinks that have mated only to, at a later time, see hemipenes on the skink that was on the bottom being mated.

Catching hemipenes everted. During introduction or mating, if you see hemipenes on any skink, you obviously know they are male.
Sometimes males will evert their hemipenes while straining to poop, and during mating season, males will often evert their hemipenes to pass spermplugs. This can happen when introduced to a female or just spontaneously.

Seeing spermplugs. Finding them passed in the tank, fresh or dry, seeing them being passed spontaneously, with or without hemipene eversion, or along with a poop, will give you 100% certainty your skink is a male.
NOT ever seeing or finding spermplugs is not proof that your skink is a female. Not all males will pass plugs, but more commonly, they are passed and dry up to remain unseen with the poop or urate or in the substrate.

Ultrasound/X-ray. If you happen to catch a mature female at the right time in her reproductive cycle, you may be able to see mature ova on an X-ray or with ultrasound. This would obviously prove that your skink is female. But just because no ova are observed does not mean you have a male, it could just be the wrong time in the cycle, or the technician may just not be experienced enough.

Proving that your skink is a female requires seeing or finding unfertilized ova, your skink delivering babies, or seeing ova on radiology. These three things are the only methods at this time by which you can call your skink a confirmed female.

Looking for male/female attributes. Very inaccurate. This is guessing at best.
Here are some of the things reportedly telling you what you have:
Broad head: male
Orange eyes: male
Brown eyes: female
Slimmer body/sides: male
Longer body: female
Broader hips: female
Seeing "bulges": male

Most experienced keepers look at the overall impression and characteristics that they have come to recognize in the different sexes. Looking at any one or two seemingly obvious characteristics can be as accurate as casting a die. There are females with "bulges", there are males with the narrowest of heads.                  Then you take into account making guesses based on photographs. Most experienced keepers can very accurately tell sex in person, but it's a whole different ballgame doing it through pictures. That's not to say that it can't be accurate, and most keepers are willing to place guesses. 

So here's what you need to do if you want to ask others for sexing opinions:
Take some pictures in good lighting with your animal laying as straight as possible on a flat surface, like the floor or a table, with it's head down --not tilted up. Take the picture from straight above, including the whole animal with its entire tail:

Copy from a post from Susann on bluetongueskinks.org

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