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

Like most reptile keepers, I have often marveled at the efficiency of snake digestive systems.  I attributed their abilities to break down bone to “powerful digestive enzymes”, but recent research has shown that, at least for Burmese Pythons (Python molurus), a far more complex and amazing process is at work.

Digesting Large Vertebrates

I’ve observed some quite large snake feasts – a Red Foot Tortoise and a 60 pound deer taken by Green Anacondas (the tortoise was an unfortunate exhibit mate; the deer fell to an anaconda at my study site in Venezuela) and 40 pound pigs regularly fed to Reticulated and Burmese Pythons under my care at the Bronx Zoo, for example.

A few shell scutes, hoofs, some bone fragments and fur where all that passed in the feces of these snakes – the rest being digested.  How do they do it?

Bone-Digesting Cells

Research at the Louis Pasteur and Indiana Universities has revealed that, after feeding, the digestive systems of Burmese Pythons undergo a dramatic transformation.  New cells are produced and worn-out cells die and are eliminated in preparation for the work at hand.

Studies of the small intestine have uncovered a new type of cell, previously unknown to science.  These cells are responsible for degrading bone and releasing its components into the snake’s bloodstream.  This process promotes efficient calcium absorption, and may be the reason that most captive snakes do not require a UVB source if fed a diet comprised of whole rats, mice and other vertebrates.

Warm-Blooded Snakes?  Not Quite, but…

We’ve known for some time now that Burmese Pythons break the “cold-blooded” rule when digesting their meals.  While most snakes must seek out a hot basking spot in order to maximize digestion, Burmese Pythons can actually raise their internal temperatures without an external heat source! 

Further Reading

Please see Big Snake Meals for some examples of how large (and unusual) snake prey can be.

To read about recent research concerning another unusual snake feeding adaptation, please see How Snakes Grow despite Food Deprivation.

An account of the original research showing that pythons can raise their body temperatures may be found in this Journal of Herpetology article.

In Part I of this article we discussed the care of the Tropical Girdled Lizard (Cordylus tropidosternum), one of the most commonly available of the 37 interesting species in the genus Cordylus (among the Girdled Lizard’s relatives is the much sought-after Armadillo Lizard, C. cataphractus, see photo).  Also known as the East African Spiny-tailed Lizard, its unique appearance and behaviors are quite captivating.  Today we’ll cover captive reproduction in more detail.

Temperature Fluctuations in Nature and Captivity

In their native South Africa, Tropical Girdled Lizards hibernate during the winter, and a cooling off period was believed necessary to induce captive reproduction.  Good results are usually achieved after captives have been held at temperatures of 58-60 F for 4-6 weeks.  During this time they move about a bit, and drink, but do not feed.

However, I’ve recently received reports of captive births (females bear 1-4 large, well-developed youngsters) among lizards subjected to little if any change in temperature. In some situations, normal seasonal fluctuations in the temperature of the room in which the lizards are held seems to be enough to stimulate reproduction.

Reproduction Without a Traditional “Winter”

In the most recent breeding of which I’ve been informed, births occurred in a terrarium maintained at an ambient of 77 F with a basking site of 95 F.  The room in which the terrarium was located was heated during the winter and air conditioned during the summer, which may have “switched seasons” on the lizards, but they bred none-the-less.

In another situation, the terrarium was in a room maintained at approximately 75 F year-round, but, being near a window, may have been subjected to the effects of outdoor temperatures.

Caring for Youngsters – UVB Light

Tropical Girdled Lizards seem to form loosely connected colonies in the wild; captives usually fare well in groups, but dominant individuals sometimes prevent others from feeding and basking.

Young lizards should have access to UVB light. However, they are quite shy, and may not bask often, especially if adults are present.  Also, they tend not to climb to the top of rock piles and such when basking, preferring to remain at or close to the terrarium’s floor – at which point they may be too far from the bulb to obtain adequate UVB exposure.  Therefore, newborns are best removed to shallow enclosures, in order to maximize UVB exposure (they should be able to bask within 6-12 inches of florescent UVB bulbs).

Useful UVB and UVA Lamps (Bulbs)

A Zoo Med 10.0 UVB bulb positioned within 6 to 8 inches of the basking site, is ideal.  Mercury vapor bulbs can be used in situations where the basking site cannot be positioned within 12 inches of the bulb.

A source of UVA light, while perhaps not critical for survival, will help to encourage natural behaviors and reproduction.

Further Reading

Recently I have helped to set up new reptile and amphibian exhibit areas for The Maritime Aquarium in Norwalk, CT (long known for its excellent collection of native marine life), and was happy to learn that Girdled Lizards have reproduced there (off exhibit).

A listing of all 37 Cordylus species, along with range and other information, is posted here.

While the role of UVB light in reptile care is well-understood, we know less about UVA.  For some thoughts and observations, please see Providing UVA to Reptiles and Amphibians.

Armadillo Girdle tailed Lizard image referenced from wikipedia and originally posted by Ltshears from flickr and Frank Wouters

Coating feeder insects with calcium and vitamin supplements is a time-tested method of adding important nutrients to reptile and amphibian diets.  However, shy and nocturnal species that do not eat soon after the insects are released into their terrariums may get little benefit from powdered supplements.  Insects quickly lose their coatings as they move about…crickets and roaches add to the problem by grooming the supplements from their bodies as soon as they are able (Yes, “grooming” …watch roaches sometime, they are quite fastidious!).

Spray-On Calcium

R Zilla Reptile Calcium Supplement Spray and Vitamin Supplement Spray help to address this problem.  The spray sticks to and may even be absorbed by insects (as well as dry foods and salad), thereby assuring its delivery no matter how much time elapses before the food is consumed.  These products will prove particularly useful to those keeping Leaf Tailed Geckos, Crocodile Skinks, Flying Geckos, Red-Eyed Treefrogs, Spadefoot Toads, certain burrowing tarantulas and others that are notoriously shy about showing themselves by day.

Calcium Spray supplies calcium in three forms, including Calcium Gluconate, which is readily utilized by many species.  It can also be administered orally to animals with deficiencies (a consultation with your veterinarian would be advisable beforehand).

Further Reading

Please see my article Providing a Balanced Diet to Reptiles and Amphibians for more information on other aspects of captive herp nutrition.

An interesting article on feeder insect calcium content is posted here.

 Next time we’ll take a look at a few effective but little-used techniques for raising the calcium content of insects fed to reptiles and amphibians. 

Agalychnis callidryas image referenced from wikipedia and originally posted by Christian R. Linder

A great many people are fearful of snakes and spiders, often to a seemingly unreasonable degree, and without any prior negative experiences.  Researchers have long sought to discover if people possess an inborn, instinctual aversion to these creatures, or if learning is involved.

Living Near Venomous Animals

My own view has always been that it makes sense for people living in the tropics to avoid all snakes and spiders, and I’ve observed that this lesson is taught to children early in life in many places.

There are still over 10,0000 snakebite deaths yearly worldwide, and in areas of high species diversity it is nearly impossible to distinguish all venomous from harmless species (in recent times, 2 renowned herpetologists were killed by snakes not know to be venomous).  On my first research project in Costa Rica, I foolishly believed that I would be able to identify many of the snakes and spiders I might encounter.  My first nighttime walk through overgrown scrub quickly taught me otherwise!

Another important point to bear in mind is that animals, especially snakes and spiders, are drawn to homes and gardens due to an unnaturally high density of prey (rodents, insects) and in search of shelter.  During the dry season in Venezuela, I collected numerous treefrogs, bats and spiders indoors.

Snakes and Primate Evolution

So, based on my experiences, I leaned toward a learning-based explanation.  However, recent work at UC Davis has revealed a possible evolutionary explanation to snake aversion among monkeys and, it is theorized, humans.

Fossil and DNA evidence indicates that large snakes may have been among the first serious predators of modern mammals, and were possibly the driving force behind the development of keen eyesight in Primates. The evolution of the Primate vision system seems linked very closely to fear and vigilance receptors in the brain.  As Primates became better at spotting snakes, snakes developed more effective camouflage, and so on.

On Madagascar, where large snakes are absent, Primates (lemurs) have not developed the excellent vision possessed by their relatives on mainland Africa.

 Most primates do indeed react with “instinctive” fear upon seeing a snake for the first time.  However, I have noticed that a great many creatures, ranging from rodents to elephants, treat novel objects with caution, however harmless they might be.

Research Involving People

Experiments involving people have yielded mixed results.  Studies conducted at the Universities of Virginia and Queensland has shown that snakes and spiders draw far more attention from human observers than do other potentially deadly animals or objects.

But many of us have (or, at least, I have!) seen toddlers squeal with delight when presented with a spider or snake…yet they will become quite scared if they see an adult express fear.

One thing I’ve noticed is that snakes and spiders have “odd shapes” (except to herpers!)…I wonder if this draws attention; and anything that moves suddenly can startle an observer, especially if it is new to that person.

Teach Them Early

It seems we must wait awhile for answers that may help people overcome their fears and view our cold-blooded friends more reasonably.  Until then, please do your part to introduce the next generation to nature early…the little guy pictured here will have no excuses for disliking herps – I’m starting him out on amphibians, and working my way up the “fear scale”!

Further Reading

You can read more about some of the research mentioned here.

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.