That Reptile Blog – Reptile, Amphibian and Exotic Pet Care and Information

With over 1,200 species, the skink family (Scincidae) is the lizard world’s largest, and in it we find some very unusual creatures.  Yet one, the Crocodile Skink (Tribolonotus gracilis), stands out as being particularly unique even in this odd assemblage of reptiles.  Originally thought to be a difficult animal to keep, we are now learning more and more about it, and captive reproduction is no longer a rarity.  Let’s take a look at how this skink distinguishes itself.

Description

This species departs radically from the typical skink body plan.  The head is enlarged, triangular in shape and capped with helmet-like scales, while four rows of thick, pointed scales line the back.  Its color is dark brown to black, with a striking red or orange area about the eye.  Crocodile Skinks average 6.5-7.8 inches in length.

Range

The Crocodile Skink is found only in Papua New Guinea and on the nearby Admiralty Islands.  One additional species, the Spiny Skink, T. novaeguinea, (which also appears in the pet trade) inhabits New Guinea, and 6 other species within the genus are found on the Solomon Islands and in New Caledonia.

Habitat

Crocodile Skinks frequent damp, shaded mountain valleys near streams and, in contrast to most skinks (and lizards in general!), they prefer temperatures of 66-75 F.

Again unlike most skinks, they are largely nocturnal or crepuscular (active in early mornings and evenings).  Although declining in some areas, recent observations indicate that piles of coconut husks on farms provide important habitat, and may help populations to increase.

Reproduction

Here again the rules are broken, with females laying only 1 egg at a time.  Oddly, the left ovary and oviduct are somewhat regressed in development as compared to the right.  The single egg developing on the left side is not laid until approximately 60 days after the right ovary’s egg has been laid.   This is true for 7 of the 8 species of Tribolonotus…Schmidt’s Helmet Skink (T. schmidti) gives birth to a single live offspring.   Well-fed female Crocodile Skinks may produce up to 6 eggs each year.

Female Crocodile Skinks guard their eggs during the 70 day incubation period.  In captivity they cover the eggs with substrate when foraging and lunge at intruders.  The hatchlings stay in close proximity to the female for approximately 2 weeks.  Further study may reveal an even greater degree of social behavior, as males kept in the same enclosure are not hostile to the young or to the female.

Other Unusual Characteristics

Crocodile Skinks are unique among lizards in having glands under the abdominal scales, on the surface of the hands, and on the undersides of the feet.  The function of these glands is not completely understood.

They also vocalize when disturbed – producing quite a loud “squawk” for such a small creature – and feign death when stressed.  I can attest that both behaviors are very surprising to the uninitiated!  Some vocalizations may be in response to egg disturbance – another lizard “first” (please see article below).

Further Reading

An interesting article detailing work carried out at the Dallas Zoo on Crocodile Skink vocalizations is posted here.

To read more about the largest lizard family, please see my article Skinks: an Overview.

A video of rarely seen display behavior is posted here.

I’ll cover the care of these most unusual lizards in a future article. 

The Desert Tortoise (Gopherus agassizi), was, in the 1960’s, a pet trade staple.  A lack of information as to its proper care and massive habitat loss has today reduced populations to alarmingly low levels.  The species is now protected, and a great deal of research has gone into its husbandry and natural history.  Yet, it seems, few appreciate just how unique this animal is.  Today I’d like to highlight some of its lesser known habits, and how they affect the future of the species.

Tortoise Diversity

Desert Tortoises are one of four tortoise species, all of the same genus, native to North America.  All are terrestrial vegetarians with forelegs modified for burrowing.

An additional 49 species of tortoises inhabit Africa (where they reach their greatest diversity), Europe, South America and Asia.  Tortoises are absent from Australia and Antarctica.

Winter Migrations

Desert Tortoises are found from southeastern California’s Mojave Desert, southwestern Arizona, southern Nevada and southwestern Utah south to northern Baja California and northern Sinaloa, Mexico, and on Tiburon Island in Gulf of California.

It is in the northern part of this range where we find a most unique winter survival strategy. Here, desert tortoises migrate to hilly areas at the onset of cold weather and hibernate in communal burrows that are 15-33 feet in length. It seems that a burrow of suitable length (over 15 feet) could not be dug by a single tortoise in one season, so these long-established burrows (and traditional migration routes) are critical to winter survival.

Effective conservation planning requires an understanding of such factors – permanent hibernation burrows may be far from the tortoises’ summer foraging areas, and thus not recognized as essential habitat when preserves are set aside.  Populations deprived of migration routes to hibernation sites will become extinct in a single winter.

Summer nights are spent in shallow, self dug burrows that are often utilized for many years.

Good Intentions Gone Bad

Another unusual impediment to Desert Tortoise conservation arose when, with good intentions, large numbers of seemingly healthy pet tortoises were returned to the wild.  These animals were responsible for introducing a virulent but difficult-to-detect respiratory illness into wild populations.  Control measures are now in place in the USA.

Desert Tortoises inhabit the centerpiece exhibit of the new reptile house at the Staten Island Zoo, which I was proud to help plan several years ago.  Please see the attached photo above, and visit if you are able.

Further Reading

A wealth of information on Desert Tortoise Conservation is posted here.

A wonderful video of a Desert Tortoise egg hatching is posted here.

Please see Parts I and II of this article for additional information on garter snake husbandry and natural history.  Today I’ll cover some often over-looked aspects of garter snake care that may help to explain why these relatively hardy snakes, and the related ribbon and water snakes, often fail to live as long as might be expected in captivity.

Thermal Gradient

A thermal gradient (varying temperatures within the terrarium) is beneficial to nearly all reptiles, but seems particularly important in maintaining the health of captive garter snakes.  This is especially true for Butler’s Garter Snakes (T. butleri), Common Garter Snakes (T. sirtalis) and others that range into the northern half of the USA.

Depending upon the species in question, garter, ribbon and water snakes do best at an ambient temperature of 72-82 F, with a warmer basking site (90-95 F) and a drop to 68 F or so at night.  Northern species should ideally be subjected to a winter cooling-off period, even if breeding is not contemplated.

UVA Light

There is some evidence that garter and related snakes (as well as Rough and Smooth Green Snakes, Opheodrys aestivus and O. vernalis), may benefit from exposure to UVA light.

A ZooMed Repti Halogen Bulb should be provided during their normal daytime cycle.  Even if not strictly necessary for survival, UVA encourages natural behavior, reproduction and, possibly, a strong immune system.

UVB Light

While snakes have not been shown to require UVB light exposure, anecdotal reports from successful garter and water snake keepers lead me to believe that these snakes may differ from most in this regard.

The Zoo Med 2.0 fluorescent lamp is specifically designed for animals needing moderate amounts of UVB light, and may be a prudent addition to the garter snake terrarium.  This bulb also supports vigorous plant growth…in contrast to most snake species, garter and ribbon snakes are very well-suited for terrariums housing sturdy live plants.

Further Reading

Laboratory guidelines concerning the importance of thermal gradients and related aspects of reptile care are posted here.

Next time we’ll cover nutrition and the care of individual garter snake species.

Once again we need to ask your help in opposing a poorly-researched effort to limit the responsible ownership of any and all pythons, including harmless species and those which have benefitted from the captive breeding efforts of hobbyists.

Senate Bill 373, which is up for consideration on this Thursday, December 3, 2009, seeks to prohibit the ownership of all snakes within the genus Python by classifying them as “injurious wildlife” under the Lacey Act.  The lack of foresight and scientific research that resulted in ball pythons being considered to be equally threatening to the environment as Burmese pythons is obvious.

In July of this year, the overwhelming response of reptile owners and the pet industry was instrumental in limiting the scope of a similar bill, HR 2811, to Burmese and African rock pythons only.  Our experience with that bill shows very clearly that our involvement in government action is critical, and that the system does work – but only if we participate in a timely manner.

It is critical that we act right now, as the Senate vote on this bill will be taken in 2 days – December 3, 2009.

The Pet Industry Joint Advisory Council has set up a simple method for you to register your opinion with the Senate here.  You can read more about the scope of the bill there as well.  Please take action now – we changed the future of our hobby and, in many cases, our professions, in July, and we can again.

For more valuable information concerning reptile hobbyists, you can also visit the US Association of Reptile Keepers (USARK).

Live plants are very useful in creating amphibian terrariums that are both attractive to the eye and beneficial for the animals housed therein.  However, amphibian skin is permeable to substances as small as oxygen molecules.  Several readers have recently questioned whether pesticides used on terrarium plants could harm amphibians through physical contact.

Examples of Contact Poisoning

Most chemicals do readily penetrate the skin of frogs and salamanders and can kill them in short order.  Pesticides on plants are a concern, even though they will not be consumed.

A coworker of mine once lost a group of Blomberg’s Toads and Smoky Jungle Frogs after confining them to quickly-rinsed enclosure that had been cleaned with Nolvasan, and I witnessed a Leopard Frog expire after being put into a pail that had previously housed a Fowler’s Toad (the stressed toad had apparently released skin toxins).

Locating Safe Plants

Some commercial growers who cater to zoos and the pet trade claim not to use pesticides.  The reptile department of your local zoo, if reachable, might be a good place to start when searching for reputable plant suppliers.  Pet stores specializing in tropical fishes usually buy pesticide-free plants as well. Some, especially those that carry plants for outdoor ponds, may stock emergent species or others suitable for use with amphibians.

Removing Surface Pesticides

If you are unsure of pesticide presence, discard the soil that arrived with the plant and rinse the plant, roots and all, vigorously.  Finish up by submerging the plant and swishing it about underwater.  Some recommend a light soap solution, but I have not found this to be necessary.

Systemic Pesticides

A greater potential concern is posed by systemic pesticides, which do not remain on the surface but rather work their way into the plant’s tissues.  Fortunately, these are not commonly used with on commercially raised plants suitable for terrariums.

One colleague of mine did run into a situation involving systemic pesticides.  He held the plants for 30 days before introducing them to his exhibits.  He had no problems with any of several tree frog species that utilized the plants frequently, and eventually used them with arboreal salamanders (Bolitoglossa spp.) as well.  This time frame is based on observation rather than rigid testing, but has proven quite dependable.

Further Reading

Those who keep herbivorous turtles and lizards also need to be concerned about potentially lethal plants.  The species listed in my article Common Plants that are Toxic to Birds  should be avoided by herp keepers as well.

To learn about growing safe plants for herbivorous reptiles, please see Reptile Gardens.