Prehensile-Tailed Skinks

Once common in the pet trade, the Prehensile-tailed (or Monkey-tailed) skink (Corucia zebrata) is becoming increasingly rare.  The skink is native to the forests of the Solomon Islands, which are unfortunately being depleted at an alarming rate.  Because of these practices, coupled with the incredibly low reproductive rate of this lizard, the Convention on International Trade of Endangered Species (C.I.T.E.S) recommended a level of appendix II in June of 2001.  This action eliminated the exportation of wild Corucia from the Solomon Isles and almost immediately made these animals very desirable for collectors. 

The natural history of the lizard is poorly understood.  What is known about the skink is mostly gained through captive observation and study.  Corucia is a large, arboreal skink that is capable of lengths of up to 32” making them the largest of all known skinks.  With this lifestyle comes an entirely prehensile tail which is used to assist in climbing and even for hanging from branches.  The strength of the animal is nothing short of remarkable, possessing even muscular digits.  The claws are more like a bird’s talons than a lizard’s claw, capable of supporting the large skink’s body comfortably in vertical or even up-side-down positions.  The head is large and heavy jawed making me at least suspect the diet in the wild includes not only various leaves, but possibly nuts and/or tree snails.  Watching the skinks feed demonstrates the incredible crushing power of the jaws and reminds one why a bite would not be a pleasant experience. 

Perhaps the most interesting feature of Corucia is the well-defined social network they establish in captivity.  The skinks are very particular about their colony and do not respond well to alterations.  Males display the male-male aggression typical of most lizards, but females are also capable (if not more so) of intra-specific conflict.  Females are reluctant to accept new females or males into their colony and often are prepared to defend the group with their own life, if necessary.  In the wild, colonies are often found within pods of trees and represent al ages and sexes.  It is reasonable to presume that the entire colony is the result of a small number of founder animals and their descendants and this “extended family” is probably not subject to diverse DNA from outsiders.  This may sound like a recipe for problems of inbreeding depression, but I actuality, probably serves to insulate the colony from random genes.  The incidence of mutation may be increased in the colony, so any natural selection must occur at the micro level.  This colonizing attribute of Corucia raises several questions that need to be addressed.  How are initial groups formed that start a colony?  How are displaced animals (such as by the pet trade) re-admitted into colonies?  How are juveniles, particularly males, treated in a colony reaching it environmental capacity? 

As an offshoot of the colonial lifestyle, the skinks have evolved a remarkable amount of parental care for their offspring.  While most reptiles care for their eggs or young only until hatching/birth and dispersion, Corucia intently protect their young for significant periods of time.  In captivity, the offspring may (and should) be left with the parents for some time following birth.  Both parents, not just the mother) will vigorously defend the baby from any perceived threat.  Additionally, the other adult members of the colony will defend any baby born into the group.  How long does this behavior continue is unknown, but in some captive cases, the other adults and the father will discontinue parental care as the skink reaches a self-sustainable size.  The mother will often continue to defend her young for their lifetime.  One of our skinks gave birth to a baby that remained in the colony and was later identified as a male.  The mother, even years later, still is very defensive of this male despite him being much larger and more powerful than his mother. 

In captivity, the most promising way of establishing a new colony is to allow juveniles to get to know each other at a young age.  If several 3-5 month olds are routinely introduced away from their colonies for brief periods, chances are good that the young can be left together permanently at a later time.  We advocate leaving baby skinks with their colony for at least six months.  During this time, the young skinks learn how to interact with others and basically learn how to be Corucia.  This means that they are accustomed to hierarchal situations and are adaptable to new circumstances.  Be wary purchasing very young skinks, as we have seen those separated at this age to have a higher tendency of becoming “rogue skinks” .  If this happens, the individual seems incapable of bonding and may require permanent, isolated housing.  These individuals seldom reproduce.

Sexing this skink can be problematic, and a multitude of techniques have been developed with varying degrees of success.  It is best to use several techniques to determine the sex of Corucia, but occasionally best guesses are still incorrect.  Methods include examining body morphology with mature males being larger with a more long, slender body and well defined head.  Mature females generally have a smaller head less distinct from the neck and a tear-drop shaped body.  One promising method for evaluating these characteristics is the C/A biometric method developed by the Leeway Corucia Research Project.  The width of the head at the widest point is divided by the width of the midsection at it’s widest point.  Results over .73 indicate a probably male and results under .73 indicate a probable female.  Males are also said to possess a v-shaped notch in the scalation just below the cloaca.  Females are said to have a straight line of scales.  Males often have bulging hemipenes during mating periods that can be seen as two cylindrical tubes pointing tail-ward below the vent.  Probing and popping should not be performed on Corucia due to the chances of damaging the lizard and their inconclusive and often confusing results.  Sexing via ultrasound is possible with adult Corucia, looking for developing ovarian follicles in females.  The most conclusive and definitive method of sexing is by endoscopy where the skink is lightly anthestitized and a small incision is made whereby an endoscope is inserted and the gonads are identified visually.  This procedure can only be accomplished by a skilled veterinarian and is out of reach for most herpetoculturists. 

Observations of the interactions of mature skinks also is a good way to sex the lizards.  A known male and unknown specimen can be introduced in a neutral setting and the reaction of the male to the other skink can be indicative of it’s gender.  The best place to do this is on an open floor.  The skinks are carefully observed and neither are in their own territory, so aggression is often minimized.  When a male is faced with another male, both will become highly agitated and will puff up with air and stand up tall.  They will often circle each other with open mouths and taking short, jabbing bites at each other.  When a female is encountered, the male will begin sniffing her quickly and pursuing her.  She may hiss and take little nips at him, but rarely will a female outside of her territory attack a male in our experience. 

All-in-all, the Solomon Island’s Prehensile-tailed skink is one of the most rewarding and interesting projects we have had the pleasure to be involved with.  Their endless array of fascinating behaviors and strong terrarium presence make them favorites for the long term with us.  Please enjoy some of our photos of these amazing reptiles.