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

The moisture content of the substrate upon which reptile eggs are incubated is a critical factor in hatching success. While certain hardy species fare well under the much-promoted technique of “squeezing water from the substrate until it barely sticks together”, many eggs require closer attention to detail.

Equipment Needed
I would like to pass along a method that I have used for hundreds of species, both in zoos and in my own collection. All that is required by way of measuring devices is a simple gram scale and a graduated cylinder (marked off in milliliters). Fortunately for me and other mathematically impaired herpers, calculations are simple – it turns out that 1 milliliter of water weighs 1 gram.

The Technique
First, determine the moisture level required by the eggs that you are incubating (please write in if you need help with this). Then, using the gram scale, weigh out enough substrate contain the eggs. You can now easily set up a ratio of, for example, 1 part substrate to 1 part water, by measuring, in the graduated cylinder, a corresponding volume of water. So, 10 milliliters of water added to 10 grams of vermiculite provides a 1:1 ratio (1:1 works well for many, but not all, reptiles).

Place the eggs (1/2 buried for most reptiles) and moistened substrate into a sealed container, weigh the container and record the weight (and date) on the cover. The cover should not be ventilated – for most reptile eggs, a once- daily check provides enough oxygen exchange (ventilation may need to be increased for large numbers of eggs once hatching time nears – please write in if unsure).

Keeping Track of Moisture Loss
Weigh the container weekly – any weight loss will be the result of evaporation, and should be made up by adding an appropriate volume of water to the substrate. For example, if the container weighs ½ gram less than the previous week, add ½ ml. of water.

The abstract of an interesting article on the conservation of moisture in reptile eggs is posted at:
http://www.springerlink.com/content/4032m356l66k66u3/

Isopods, more commonly known as sowbugs, pillbugs or potato bugs, are a valuable but largely neglected food source for pet amphibians and reptiles. The over 10,000 described species are common in most habitats worldwide, and are therefore an important in the diets many creatures. Ranging in size from .02 to 20 inches, there is an isopod to fit every feeding need (public aquariums pay $600 or more each for giant, deep-sea forms, so don’t plan on feeding these to your monitor lizards!).

Nutritious, Interesting Scavengers
Isopods are crustaceans, and as such provide a variety of nutrients not to be found in insects. Another thing I like about using them has to do with their appetites – they will eat anything, so by feeding them a rich and varied diet you are improving their value as food items for your pets. Furthermore, native sowbugs and pillbugs will live in most terrariums and are valuable scavengers, relishing dead earthworms, crickets and feces. I always include a group in naturalistic habitats that I design for zoos and museums. Finally, they are very interesting to observe in their own right. They do contain quite a bit of chitin, so are not suitable as the sole item in a diet.

Obtaining Isopods
Temperate isopods prefer cool, moist environments, and so are most easily found in spring and fall. You can collect them below rocks and leaf litter. They will also flock to cover such as boards placed on the ground, especially if the area is kept moist and baited with coffee grounds or ripe fruit. Biological supply houses also sell starter cultures.

Keeping and Breeding Isopods
Keep your colony in a vented plastic container with 3-4 inches of R-Zilla Coconut Husk as a substrate. Plastic terrariums by Lee, Tom Aquarium, Hagen and PLA House make ideal isopod homes. Be sure to keep the bedding moist but not wet. A covering of Zoo Med Terrarium Moss will help retain moisture and offer shelter to the isopods, making collection easier.

A mix of R-Zilla Alfalfa Meal Bedding and Tetra Min Flake Fish Food is an excellent basic diet, to which can be added grass clippings, leaf litter, coffee grounds and almost any fruit or vegetable. A cool basement makes an ideal location for the colony, but average room temperatures are fine. Be sure to keep an eye on moisture levels during hot, dry periods. A breeding colony will supply huge numbers of isopods of all sizes.

My Experience
I have always kept an isopod colony for my collection, and have used them in zoos as well. They are easy to maintain, breed readily and are, I think, one of the best-kept secrets (no more!) in herptoculture. Very few insectivorous herps refuse them, and they are readily taken by many fishes and birds as well. Be sure to try a group in your naturalistic terrariums also, as they make fine scavengers and, unlike crickets, they will not attack debilitated pets.

The University of Arizona’s Center for Insect Science Education offers a wealth of information on native invertebrates in the wild and captivity. Read more about isopods at:
http://insected.arizona.edu/isoinfo.htm

Click: The Monitor Lizards (Family Varanidae) – Family Overview and Species Accounts; – Some Interesting Monitors and Their Care – Part I, to read the first part of this article.

Merten’s Water Monitor, Varanus mertensi
The popularity of this most aquatic of the world’s monitor lizards is soaring, and with good reason – it is active, hardy, of manageable size (averages 3 feet in length, occasionally to 4) and very responsive to its surroundings.

Range
Native to northern and western Australia (Northern Territory, Queensland, South Australia and off-shore islands), Merten’s water monitors frequent creeks, rivers, canals, ponds and reservoirs. They bask on the shore or low overhanging branches, and rarely stray far from the water’s edge. Although common at present, this situation may change – water monitors readily consume introduced marine toads, and many are killed by the amphibians’ toxins.

Unique Adaptations
Merten’s water monitors, named after eminent Russian-born herpetologist Robert Mertens (1894-1975) of Frankfurt Germany’s Seckenberg Museum,
are deep brown to black in color, with dark-edged cream or yellow spots. The tail is laterally compressed and the nostrils, which can be sealed during dives, are located high on the snout.

Housing
Water monitors require a spacious cage (at least 4’x4’x 3′), a UVB source and a large (preferably drainable) pool. They must be able to bask at 90-95 F and to dry off completely upon leaving the water.

Diet
The natural diet consists largely of crabs, crayfish and fish, but frogs, tadpoles, turtle and other reptile eggs, shrimp, snails, nestling birds, planigales and other small mammals, large insects and carrion are also taken. They have been observed foraging in dumps, with discarded sausages apparently being a favored food! Water monitors use their tails to concentrate small fishes when hunting in the shallows.

Captives should not be fed a rodent-based diet, but rather one weighed heavily in favor of whole, fresh-water fish, whole, unshelled prawn, crayfish, roaches, crickets, earthworms, and canned insects/monitor diets . Pink mice are preferable to furred rodents, and should be offered only once each week or two. This species seems to have a quite high metabolism, and does best when fed small meals every 3-4 days.

Blue Tree or Blue-Spotted Tree Monitor, Varanus macraei
This strikingly colored lizard only appeared in zoos in the late 1990’s, and was not named as a distinct species until 2001. Never-the-less, beauty and small size (to 40 inches) has propelled it to the top of the “most desired species lists” of many monitor fanciers.

These slender monitors are jet black in color and variably patterned with blue spots and bands. The prehensile tail comprises 2/3 of the animal’s length.

Range
Blue tree monitors are found only on Batanta Island, Indonesia (off Irian Jaya, New Guinea). Almost entirely arboreal, they inhabit trees and shrubs within rainforests and estuarine swamps. Their wild status is unknown, but the species is listed on CITES Appendix II due to the extremely limited natural range.

Housing
Blue tree monitors require a spacious cage with provisions for climbing, UVB light and a basking spot of 90-95 F. The several pairs I’ve kept have co-existed without incident, and frequently rested in close contact with one another. Quite shy and quick to take flight, they do best in a well-planted cage provided with numerous hideaways and located in a quiet area. This is a species to observe, not handle.

Diet
The natural diet is likely composed largely of invertebrates such as tree crickets, katydids, snails, caterpillars and spiders, along with occasional treefrogs, lizards, small birds and their eggs, nestling mice and other small mammals.

As with other small monitors, I prefer not to feed too many rodents to this species. Mine thrive upon waxworms, crickets, crayfish, super mealworms, roaches, chicks and quail eggs. Pink mice are given every two weeks or so. Canned insects and monitor diets are often accepted and should be included as a source of dietary variety.

Breeding
Females lay 2-6 eggs at a time, and may produce up to 6 clutches per year (this may be a function of food availability in captivity). The young average 5 inches in length and hatch after an incubation period of 200-225 days. Captive females will bury eggs within moist substrates on the ground but seem to prefer arboreal nest boxes.

An Escapee that Made the Most of His “Vacation”
The long, slender tail of this monitor is prehensile and adds to its climbing abilities and agility. Alert and quick moving, blue tree monitors can catch even the swiftest of prey in their treetop homes. One individual that escaped from an exhibit at the Bronx Zoo was in the process of swallowing a house sparrow when I recovered him from atop a vine-covered fence!

In depth information about the family Varanidae and its individual species is posted at:
http://www.tigr.org/reptiles/families/Varanidae.html

Note: Please see The Monitor Lizards (Family Varanidae) – Family Overview and Species Accounts
for information on the natural history of monitor lizards.

Storr’s Pygmy Monitor, Varanus storri
This is the smallest monitor regularly available in the pet trade.   Also nearly the tiniest member of the family Varanidae, this species has much to recommend it as a “first monitor”.  Reaching just 14 inches in length, Storr’s monitor is one of the only monitors that can be housed within an aquarium-sized (see below) enclosure when adult.

A Popular Pet
Storr’s monitors are immensely popular because they combine all of the typical monitor traits in a small package – indeed, they act exactly like tiny versions of their larger cousins.  What they lack in size is more than made up for in attitude, and they are quite bold as captives.  In fact, keeping more than one in a cage, even a mated pair, is difficult due to their aggressive natures.

Range
This plucky, brown little lizard hails from northeastern Australia.  A subspecies, reddish in color but otherwise similar (V. s. ocreatus) ranges further west.  In the eastern part of its range, Storr’s monitor is threatened by the introduced marine toad, which both preys upon and competes with it.  Populations have all but disappeared from some areas already.

Housing
Storr’s monitors are quite active and should be housed in a tightly secured aquarium of at least 30 – 55 gallons (“long models are best”).  They require a source of UVB light  and a basking site that reaches 90 F or so.

Diet
Although they are often fed pink mice and small rodents in captivity, the natural diet of this species consists largely of insects.  The bulk of their food in captivity should be roaches, crickets, waxworms, super mealworms, mealworm beetles and wild-caught insects.  Canned insects, such as silkworms and grasshoppers, offer an excellent source of dietary variety.  Many individuals also accept canned monitor diets.

Breeding
Captive breeding is possible, but pairs must be watched closely for aggression.  The 2-5 eggs hatch in 100 days at 82F.

Crocodile Monitor, Varanus salvadorii

At the other end of the spectrum from Storr’s monitor is southern New Guinea’s massive crocodile monitor – it approaches 9 feet in length (nearly as long as, but much lighter than, the Komodo dragon), and there are unverified reports of much longer individuals.  The prehensile tail is twice as long as the snout-vent length.  Crocodile monitors are black in color and boldly marked with yellow spots, and sport long claws and a bulbous snout (particularly so in mature males).

Range
Highly arboreal despite their size, crocodile monitors dwell in the canopies of lowland forests in the vicinity of rivers and mangrove swamps.  Little is known of their status in the wild, but there is concern given the limited range; the species is listed on CITES Appendix II.

Warning!
In contrast to the other lizards described here, crocodile monitors are suitable only for very advanced hobbyists, or as zoo animals.  Those I worked with learned to tolerate my presence, but remained wary and agressive even after many years.

In contrast to the usual structure of monitor teeth, those of the crocodile monitor are serrated and over-lapping – possibly an adaptation to holding onto and carrying large prey high above the forest floor.  These animals are formidable predators, and capable of inflicting potentially life-threatening wounds.

Housing
Captive-bred animals are available and adjust moderately well (please see above) if given huge, high-topped enclosures that accommodate their arboreal lifestyles – forcing crocodile monitors to remain on the ground is, in my experience, quite stressful to them.

A cage or room of 10’ x 10’ by 10’ would be required for a single adult.  UVB light and a basking spot of 90-95 F are needed.  A humid environment is preferred, but they must be able to dry off as well.

Diet
Wild crocodile monitors feed upon cuscus, young tree kangaroos, naked-tailed rats, bandicoots, bats and other mammals, birds and their eggs, frogs, snakes, lizards and carrion.  Captives do well on rats, mice, chicks, crayfish, large roaches and hard-boiled eggs.

Image referenced from Wikipedia.

Check back on Friday for more Monitor Species Profiles.