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

Introduction
Herpetologists and hobbyists alike have long known that there is something “different” about the family of lizards known collectively as “monitors” (or, in Australia, “goannas”).  One cannot observe a monitor for long without getting a sense of the animal’s intelligence – they scrutinize the world differently than do other reptiles, and their reactions to new situations are surprisingly quick and complex.  Recent studies have confirmed that monitors are unique, and, in many ways, the most intelligent and advanced of the lizards.

In years past pet keepers were limited to a very small number of monitor species from which to choose.  An explosion of interest in the group has radically changed that situation, and today animals rarely seen even in zoos are being commercially bred in huge numbers.  Happily, there are monitors even for those without much room – and the very smallest types still exhibit true monitor behavior, intelligence and “attitude”.

Today I’ll present an overview of the group as a whole.

Species Diversity
Sixty eight species of monitor lizards, all classified within the family Varanidae and the genus Varanus, range across Asia, Africa and Australia.  Although generally associated with warm climates, one species, the desert monitor (V. griseus) may be found as far north as Kazakhstan – at roughly the same latitude as southern Vermont.

In Australia, where over 2/3 of the world’s species are found, monitor lizards have evolved to fill a wide range of ecological roles held elsewhere by other lizards and by large, predatory birds and mammals.  Huge Australian species such as 8 foot long parentie monitor, V. giganteus, and the lace monitor, V. varius, are the dominant predators in their habitats,  as are Komodo dragons, V. komodoensis, on the islands of Komodo, Padav, Rinca and Flores.

At 8 inches long, the short-tailed monitor, or pygmy goanna,
V. brevicauda, is the smallest member of the group.  The infamous Komodo dragon is the world’s largest lizard.  It occasionally tops 10 feet in length, but is dwarfed by extinct monitor species which may have measured over 20 feet long.

General Physical Characteristics
All monitors share a similar body plan – a long neck and relatively small head, sturdy body and limbs and a long, powerful tail, and most measure in the range of 2 to 5 feet in length.

The tongue is deeply forked and is flicked out repeatedly.  As with snakes, the tongue carries airborne chemical cues to the Jacobson’s organ, thus conveying information about the environment and other animals.

Male monitor lizards compete for females by grappling, often rising onto their hind legs during tests of strength.  All species lay eggs.

Diet
All monitors are alert, effective predators, with the various species taking an incredibly huge array of prey – termites and other insects, snails, spiders, crayfish and other invertebrates, birds and their eggs, frogs, turtles, snakes, hatchling crocodiles and other reptiles and amphibians, and rodents, weasels, tree kangaroos and other mammals to the size of adult deer.  Large monitors living near developed areas also prey upon domestic dogs, cats, chickens, ducks, pigs and goats, and consume carrion and offal as well.  The Philippine monitor lizard, or bataans (V. olivaceus), is unique in feeding upon fruit at certain times of the year.

On rare occasions, the Komodo dragons have attacked and killed people.  In fact, current restrictions on the long-held tradition of feeding goats to these huge lizards (a tourist attraction with possible links to local religious beliefs) is possibly at the root of the recent rise in attacks on people and livestock.

Habitats
Monitor lizards have evolved to occupy a wide variety of habitats – there are arboreal specialists, such as the green tree monitor, V. prasinus, aquatic species such as the mangrove monitor, V. indicus, and grassland dwellers such as the savanna monitor, V. exanthematicus.  There are also many generalists – Gould’s monitor, V. gouldii, a large lizard that occupies nearly all of Australia, is equally at home in grasslands, open forests, river valleys, cliff-sides, semi-deserts and nearly all other habitats within its huge range.

The Nile monitor, V. niloticus, is native to sub-Saharan Africa but is now thriving in southern Florida, where released pets have established breeding populations.  Approaching 7 feet in length, this aggressive predator is severely impacting the local ecology by out-competing and preying upon a wide variety of native species.

Wide-Ranging and Isolated Species
The size of the ranges of the different species varies greatly in extent.  For example, the blue tree monitor, V. macraei is limited in distribution to Batantan Island off Papua New Guinea while the 9 foot long Asian water monitor, V. salvator, is found from India through Bangladesh, Myanmar, southern China, Vietnam, Laos, Cambodia, Thailand, the Philippines, Malaysia and Indonesia.

Harvard biologist David Blachurn knew he was onto something unusual when a benign-looking frog he was examining in Cameroon, West Africa kicked out and left him with a bleeding cut.  Unusual indeed – an article  (23 August 2008) in Biology Letters describes the hidden claws of Perret’s night frog as the only vertebrate claws known to break through the skin in order to become functional.  Some, or possibly all, of the other 10 frogs within the genus Astylosternus are also equipped with skin-covered claws on their toes (the fingers are clawless).

The frog’s sharp, curved claw is actually the last bone of the toe, and pierces the toe’s skin when a specific tendon is flexed.  It is assumed that the claw retracts after use and the skin heals, but further study is needed.  Other amphibians that experience “self-inflicted” wounds include the Surinam toads, Pipa spp., whose young push through the skin of the female’s back when ready to swim off on their own and the ribbed newt, Pleurodeles waltl.  The ribs of this newt pierce the skin of the back, carrying toxins with them, when the animal is threatened.

Despite the massive trauma caused by the emergence of 80+ fully formed little frogs, the skin of breeding Surinam toads (P. pipa) under my care appeared well-healed within 24 hours.  I’m sure there are some compounds that may be of medical use to people hidden in the body chemistry of this and other amphibian species.

Of course, people living within the habitat of Perret’s night frog have long known of its odd defense and even utilize specially-constructed spears when hunting it, to avoid being injured.

The only other frogs known to have claws are members of the family Pipidae – the various African clawed and dwarf African clawed frogs.  I have observed both putting their claws, which are always exposed, to interesting uses (more to come in future articles).

You can read more about this frog and related species at:
http://research.amnh.org/herpetology/amphibia/references.php?id=1191

During our last look at outdoor ponds  I discussed an ideal amphibian inhabitant, the American bullfrog.  Today I’ll introduce a reptile that is equally at home outdoors, the red-eared slider.

A Better Outdoor Than Indoor Pet
The Red-Eared Slider is the world’s most popular pet turtle.  The small green hatchlings were previously sold by the millions throughout the USA, but government restrictions have now limited the availability of animals under 4 inches in length (pending legislation may change that situation in the future).

However, sliders are not well suited to indoor aquariums, as they are very active and females can reach a shell length of 12 inches or so.  A turtle of that size needs a tank of at least 55-75 gallon capacity, along with a very powerful filter to maintain water quality.  Even in aquariums of that size, however, these vigorous turtles are cramped.

Sunlight and Diet
Sliders make interesting, attractive inhabitants of garden pools if given enough space and easy access to sunny basking spots. Like most turtles, they require unfiltered sunlight in order to form the vitamin D that is necessary to process calcium and build strong shells (exceptions to this rule are certain largely aquatic, non-basking species, such as snapping turtles, musk turtles, and soft-shelled turtles).

Red-eared sliders will readily consume Repto-min, earthworms, crickets, mealworms, prawn and canned insects, and will do their best to catch small fishes and tadpoles.  They usually will coexist quite well with larger goldfish and sunfish, if there is ample room for the fish to avoid the turtles.  Adults may consume some types of pond vegetation, but if provided with romaine, dandelion, kale and other greens, they will often leave ornamental plants alone.

Other Turtles
Other turtles of similar habits that do well in outdoor ponds are the Eastern painted turtle, Chrysemys picta picta (and subspecies, such as the Midland, Western and Southern painted turtles) and the various Map Turtles, Graptemys spp.  The largely aquatic musk turtle, Sternotherus odoratus, does well even in quite small pools.

Enclosing the Pond
Semi-aquatic turtles often remain near their pond, even if it is unfenced, but males may move away in search of females during the breeding season, and gravid females will seek out suitable nesting areas.  Bear in mind also that raccoons are very adept at preying upon even quite large turtles.

Useful information on constructing and maintaining an outdoor turtle pond is posted at:
http://www.tortoise.org/general/pondmak.html

Click: The Marine or Cane Toad, Bufo marinus (Rhinella marina) in Nature and Captivity – Marine Toads as Pets – Part 1 to read the first part of this article.

Many pet keepers feed their toads heavily on pink and even adult mice. This is a bad idea and will eventually lead to eye, kidney and liver problems. While these aggressive predators certainly take the occasional rodent or lizard in the wild, research has shown that insects, spiders and other invertebrates form the vast majority of their natural diet. In captivity, a goldfish, minnow or shiner can be offered every month or so, perhaps a pink mouse every 6-8 weeks, but limit their intake of vertebrates. Do not feed mice other than pinkies – toads swallow their food alive, and sooner or later they will be injured by a mouse’s sharp teeth.

Marine Toads take readily to tong or even hand feeding (use plastic tongs). Canned insects, such as Can O’ Grasshoppers and Can O’ Pillars should be hand-fed to increase dietary variety.

Wild caught insects, collected from pesticide-free areas, should be offered whenever possible. Zoo Med’s Bug Napper is an excellent insect trap. Sweeping a net through tall grass and searching around outdoor lights will also yield a wide variety of tasty treats. Avoid using spiders, stinging and brightly -colored insects and fireflies, and do not collect during times when your area is being commercially sprayed for mosquito control.

My Marine Toads relish cicadas, katydids, grasshoppers, beetles of all types, moths, tree crickets, caterpillars, sow bugs and most everything else I come up with. Most of my amphibians feed largely upon wild-caught invertebrates throughout the summer, but even a few beetles plucked from a screen door every night or so will go a long way in keeping your pet in the peak of health.

Social Groups
Marine Toads coexist fairly well together, but bear in mind that they need a lot of room and must be kept scrupulously clean. Fighting is rare, but large animals will out-compete smaller ones for food, so hand-feed if in doubt.

Captive Longevity
The published longevity record is 24 years. Two that I acquired as adults are, at last report, still going strong after 16 years.

Handling and Enrichment
Marine Toads learn very quickly where their meals lie, and will soon greet you as you approach their terrarium. They do not enjoy being held, however, and like all amphibians are subject health problems once the skin’s mucus covering is removed. Handle them – carefully and with clean, wet hands – only when necessary.

Toads in general and this species in particular secrete extremely virulent skin toxins and must be treated with care. Always wash thoroughly after handling them, and never touch your mouth or eyes before doing so. Do not handle Marine Toads if you have a cut in your skin, no matter how tiny it may be. Children and pets must be prevented from coming in contact with these animals, to the point of installing a lock on the terrarium if you are at all unsure. Toads that are licked or swallowed can cause life-threatening reactions.

Marine Toads benefit from hunting opportunities, and remain much more active and alert when provided such on a regular basis. Allow non-threatening insects (crickets may chew on cold or debilitated animals) such as caterpillars, katydids and grasshoppers to roam about their tank when possible. Better still, set your toads up in a secure area outdoors near some over-ripe fruit (to draw beetles and butterflies) or a bush crawling with caterpillars, sit back and enjoy!

Breeding
Egg-laying in the wild is generally in response to the onset of rainy periods, and such may occur if the toads are provided with “artificial rain” in captivity (more on this in the future). Captives sometime breed spontaneously as well. The tadpoles are fairly hardy – please write in if you are fortunate enough to have a breeding pair.

Miscellaneous
In some situations, Marine Toads fare well in semi-freedom. They stay quite close to favored territories – the same 5-6 individuals hunted outside my kitchen in Costa Rica every night for several weeks.

While working at the Bronx Zoo, I kept a few at liberty below a row of exhibits, and another small group in a greenhouse. Here they fed upon crickets, roaches, centipedes, spiders and the like, and grew quite fat. They never failed to emerge from their shelters when I arrived each morning, waiting in a semi-circle for the treats (earthworms and crayfish) they had come to expect. They really are among the most responsive of the amphibians – I highly recommend one if you have the space.

A great deal of information about Marine Toads is posted at:
http://www.globalamphibians.org/servlet/GAA?searchName=Bufo+marinus

General
I have always found Marine Toads to be among the most engaging of amphibian pets.  Toads in general seem to be (externally at least) more responsive than frogs- they “watch” everything, and appear to deliberately consider their next move.  Protected as they are by powerful skin toxins, Marine Toads in particular seem possessed of real “confidence” in captivity, and we can get to know them well if we take the time.

Please see Marine Toads – Natural History for information on Marine Toads in the wild.

Enclosure and Physical Environment
Some Marine Toads grow quite large – to 10 inches, and even small individuals can be quite active and consequently need a large terrarium.  An averaged-sized adult can be kept in a 30 gallon “long” aquarium – while a really large one or a pair will do best in a tank of 55-75 gallon capacity.

During warm weather, Marine Toads can be housed in secure outdoor enclosures as well.  Insects lured by a small light or over-ripe fruit will supply your toads with important dietary variety.

Their enclosure should be topped by a screen cover secured by clamps  and the substrate should be kept damp but not wet.  Compressed Frog Moss, Fir and Sphagnum Moss Bedding and Reptile Cage Carpet all work well.  Marine Toads have a tendency to swallow substrate when feeding – usually they pass this without incident, but tong-feed your animals or use a feeding bowl –prod- if you notice this happening frequently.

Despite being quite bold, Marine Toads require a hide-a way where they can get out of sight (Rock Den or Turtle Hut).  Be sure to provide a cave for each of your toads, as animals that cluster in one shelter seem prone to fungal infections of the skin.

Marine Toads need to soak frequently, so always have a bowl of de-chlorinated water available.  Be sure that small toads can exit the water bowl easily, as they are poor swimmers.

While small toads can be kept in planted exhibits, adults will mangle all but the sturdiest of plants (try Cast Iron Plants and Snake Plants).  They will clamber about on smooth logs – just be sure that these are secured in place as these brutes are quite strong and may roll a log onto themselves or a tank-mate.

Light, Heat and Humidity
Marine Toads do not require UVB radiation, and so will get along with a regular fluorescent bulb.  Use a low UVB output plant light if you keep live plants, as high levels may cause eye damage.

The terrarium should be maintained at 72-80 F.  Marine Toads can tolerate much warmer conditions – I have uncovered them below boards at temperatures of 100 F – but such is stressful and should be avoided.

Despite being largely terrestrial, Marine Toads seem quite prone to desiccation – spray their terrarium each morning and keep a water bowl available at all times. They often defecate in the water bowl – be sure to clean this as soon as possible, lest they absorb ammonia and other toxins through their skin.

Feeding
Your pets should be given as much dietary variety as possible.  I have observed wild Marine Toads consuming over 2 dozen insect species in a very short time, and other researchers have documented a huge range of prey items (please see Marine Toads – Natural History article).

The main portion of their diet should not be crickets, but rather a mix of earthworms (these can be used as the bulk of their diet if necessary), roaches, crickets, and waxworms.  Silkworms and Tomato Hornworms, available via internet dealers, should be offered from time to time.  I use super mealworms sparingly, but others have done so frequently without incident.  I have found crayfish to be an important food item for a wide variety of creatures, including Marine Toads.  I remove their claws, just to be on the safe side.

Adults fed a varied diet require a vitamin/mineral supplement  only once each week at most.  The food of growing animals should be supplemented 2-3 times weekly.

Check back Wednesday for the conclusion of Marine Toads as Pets.