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In the previous issue of IGUANA, we presented Captive Care
of Monitors, Part I: Introduction and Housing. Part II follows.

Diet

Almost all monitors are carnivorous, that is, they are exclu-
sive meat eaters. Two notable exceptions are Varanus oliva-

caeus and the newly described V. mabitang, both of which live in
the Philippines and prefer to eat fruit and leaves (Auffenberg
1988, Gaulke and Curio 2001). Insects, spiders, crayfish, fish,
amphibians, reptiles, eggs, birds, and mammals make up the
bulk of the diet of most monitors. Prey size and type generally
depends on the size of the monitor. In the wild, monitors, par-
ticularly V. niloticus, V. gouldii, and V. panoptes, are known to
find clutches of eggs of other monitors or crocodiles (Bayless
1992, Lenz 1995). In general, monitors do not appear to be par-
ticularly selective regarding food. Occasionally, they are even
cannibalistic. Varanus komodoensis, from Komodo Island, not
only feeds on pigs, which occur on this island, but also takes Red
Deer and other feral animals. Humans also have fallen prey to
the Komodo Monitor.

Because size varies considerably between species, the food
spectrum is also highly variable. In the wild, members of the
smaller species feed mainly on insects and smaller reptiles, which
they can overpower. The examination of stomach contents from
wild monitors has revealed the preferred food items of some
species (James et al. 1992, Losos and Greene 1988, Pianka

1968, 1969a, b, 1970a, b, c, 1982, Shine 1986, Sprackland
1993, Ziegler and Böhme 1996, Gaulke and Curio 2001).

The variety of food available to captive monitors is much
more limited. Common food items suitable for smaller species
include crickets, grasshoppers, locusts, cockroaches, and larvae
of the giant mealworm. Newborn mice (thawed or recently
euthanized) are occasionally offered to expand the menu. Any
captive diet lacks the balanced mixture of vitamins, minerals,
and fiber available in the wild, thus supplementation is neces-
sary to provide these nutrients. All insect prey should be dusted
with a vitamin and mineral mixture such as Nekton MSA® or
Miner-all®. Do not offer too much food, especially crickets and
cockroaches, as they tend to hide within the furnishings of the
cage, where the monitors cannot reach them. Unconsumed noc-
turnal insects also may represent a physical risk to the sleeping
monitor. To date, no reports have documented crickets attack-
ing healthy monitors, but evidence suggests that crickets in a
cage have consumed dead monitors. The risk of injury, especially
for young offspring, should not be overlooked.

Larger monitors require larger food items. Feeding a lizard
the size of a V. mertensi on crickets and locusts is prohibitively

246 IGUANA  •  VOLUME 12, NUMBER 4  •  DECEMBER 2005 EIDENMÜLLER

H U S B A N D R Y

Captive Care of Monitors
Part II: Diet and Reproduction1

Bernd Eidenmüller

Frankfurt am Main, Germany

Photographs by author.

Grasshoppers make an appropriately sized meal for the Pilbara Monitor
(Varanus pilbarensis).

A Dwarf Monitor (Varanus storri) at mealtime.

1 Adapted by AJ Gutman from B. Eidenmuller, Monitors: Natural
History — Captive Care — Breeding. Herpeton Verlag, Offenbach,
Germany. 



IGUANA  •  VOLUME 12, NUMBER 4  •  DECEMBER 2005 247MONITORS

expensive. Mice, and occasionally rats and chicks, are much
more appropriate food items. The unit price is low and the pro-
tein more concentrated so less total food volume is required.
Feeding chicks has at least one drawback for the keeper; it tends
to result in monitor excrement that is very runny and smells
unpleasant. If you feed monitors on chicken, the enclosure
should be cleaned immediately for hygienic reasons. Canned
dog or cat food should not be fed to captive monitors as these
products contain too much protein and are very low in miner-
als and fiber. ZuPreem (Premium Nutrition Products, Inc.) pro-
duces a canned monitor and tegu diet that provides the proper
balance of nutrition.

Conditioning for Breeding
All monitors live a solitary existence in the wild and, in captiv-
ity, should be maintained singly or at most as pairs. In order to
synchronize pairs of animals sexually, I recommend an occa-
sional period of separation. Separations lasting between four
weeks and three months can be carried out several times during
the year. Similarly, a brumation period lasting between one and
three months, with an ambient temperature of approximately
15 °C is appropriate for animals from colder areas (e.g., for
monitors from the southern parts of Australia or South Africa).
A period of quiescence also will simulate a summer aestivation
for animals from a tropical climate (e.g., V. mertensi or V. acan-
thurus), thereby promoting synchronization of the sexes and
post-hibernation breeding. Another possibility is the introduc-
tion of a rainy season that simulates the conditions required by
animals from the equatorial rain forests (e.g., V. prasinus). 

A hibernation or aestivation period is comparatively simple to
adopt in captivity by continuously reducing both the photope-
riod and the amount of time that heat is supplied to the lizards
over a winter rest period. In the middle of winter, the animal
does not require significant heat and illumination within its
enclosure. Therefore, a spotlight that is switched on for short
periods of time for the animal to bask is sufficient. Throughout
this period of relative dormancy, animals should always have a
bowl of fresh drinking water available in the enclosure, so that

Large food insects can pose a hazard to hatchlings such as these Timor
Monitors (Varanus timorensis).

This Mangrove Monitor (Varanus indicus) has just eaten a mouse.



when they wake up, they are able to drink. A real hibernation,
in which animals are maintained without light and heat over
long periods of time, is neither required nor recommended for
any monitor species. When an animal enters this period of dor-
mancy during the colder months, little other care is required
until it emerges with the onset of warmer months. Most animals
will survive this period in their hiding places and remain inac-
tive. Animals should not be reactivated too quickly when the
weather warms. They will note the change in climatic conditions
and gradually over a period of days and in some cases weeks,
reappear to seek a basking site and food. After they have recom-
menced basking over a few days, food can be offered.

Monitors from a tropical rainforest environment (e.g.,
members of the V. prasinus complex and V. scalaris from Cape
York Peninsula) do not require the above-mentioned hiberna-
tion period. A rainy period can trigger mating behavior. The
entire enclosure can be moistened two or three times a day with
water from a spray bottle to simulate a rainy season. This will
raise the humidity, as will a water basin placed in the enclosure
on top of an under-tank heating mat. Ultrasound humidifiers

can increase humidity during the day by repeatedly switching
on and off. These are very effective, but generally expensive.

Reproduction and Egg Husbandry
If pairs of monitors have been maintained together for some
time and they appear compatible, these animals may be suc-
cessfully bred to produce clutches of eggs and healthy offspring.
The time between the last observed mating and egg-laying in
most monitors is between four and eight weeks. An exception
seems to be V. mertensi. In this species, the time appears to be
three weeks between mating and egg-laying. After mating activ-
ity has ceased, the female should be allowed to bask and obtain
food as needed; therefore, after mating behavior has stopped, the
male should be removed from the enclosure. This is particularly
important for V. prasinus, because these animals are very stress-
sensitive, even outside of the mating season. The high stress
induced by contact with conspecifics is an indication that mem-
bers of this species are generally found as solitary individuals.

Prior to egg-laying, females show an increase in body size,
becoming more rotund. At this stage, a suitable egg-laying box
should be offered. The size of the egg-laying box should be suited
to the size of the animal (e.g., a box 40 x 25 x 20 cm, LWH is
sufficient for V. acanthurus). For larger species, the egg-laying box
should be proportionally larger. Bird nesting boxes have been
used successfully for V. prasinus; these can be natural hollow logs
with a cap on each end and a hole part way down for entry
(Eidenmüller 1996, Eidenmüller and Wicker 1992) or made of
plywood (Dedlmar 1994). These nests are filled with lightly
moistened bark mulch or vermiculite. Irrespective of whether the
box is made of wood or plastic, the animal must be able to gain
access to it from above. The box must be light impermeable,
show a thermal gradient ranging from about 30 °C at the top to
about 25 °C at the bottom, and the substratum must contain suf-
ficient moisture to prevent desiccation of the eggs before they can
be removed and incubated elsewhere. In some cases, the place-
ment of a piece of cork bark on the substratum in the box may
be helpful. This serves two purposes, first, it will allow little light
into the burrowing material (bark mulch, sand, or vermiculite),
and second, the digging animal gains a sense of security that the
walls of her nest burrow will not collapse.

248 IGUANA  •  VOLUME 12, NUMBER 4  •  DECEMBER 2005 EIDENMÜLLER

Emerald Tree Monitors (Varanus prasinus) mating on the back wall of
their terrarium.

Bird nest boxes have proven to be acceptable egg-laying sites for tree
dwellers such as Varanus prasinus.



IGUANA  •  VOLUME 12, NUMBER 4  •  DECEMBER 2005 249MONITORS

Many monitors cease feeding prior to egg-laying. While
food denial is not a sure sign of forthcoming egg-laying, it is nev-
ertheless a good indicator that a lizard is gravid. If an animal
does cease to feed, access to the egg-laying chamber is impera-
tive. A substantial amount of energy is used during reproduc-
tion, and food must be available to the exhausted animal after
oviposition. The tail base and thigh musculature have generally
collapsed. Egg-laying is a stressful time and can be accompanied
by problems.

In general, stress is the single greatest factor that can lead to
difficulties in husbandry during reproduction. For example, ani-
mals that have not laid in the prescribed time are likely stressed
by some unseen and intangible factor that can be very difficult
to ascertain. Possible conditions that can result in an animal fail-
ing to lay eggs include the nest box not being in place or in an
inappropriate position, a male still present in the cage, insuffi-
cient nest humidity, or that the keeper had spent too long view-
ing the animal. Stress factors must be teased out by a process of
elimination.

Most monitors undertake test-diggings for suitable egg
chambers some days before actually being ready to deposit eggs.
As soon as they stop test-digging and refuse food, egg-laying is
nigh. Similarly, the collapse of the tail base and thighs may indi-
cate imminent ovipositioning. If the monitor has been digging test
holes for some time and then ceases all activity at a time when you
are confident she should be laying but has not yet done so, med-
ical help should be consulted. This is the single largest indicator
that something has gone wrong. Often a qualified veterinarian can
induce egg-laying using the hormone oxytocin. If, however, egg-
laying is long overdue, a Caesarean section may be needed.
Examples of a prolonged egg-laying period include clutches of
both V. acanthurus and V. scalaris that were only partially laid, with
the remaining eggs becoming bound to the oviduct. Surgery was
required to save the female and ensure her reproductive health for
subsequent years. This is only one of many situations that can arise
when egg-laying in a monitor is overdue. If egg deposition is
weeks overdue, I can only suggest that the animal be placed in the
care of a reliable reptile veterinarian.

Incubation
As soon as the eggs have been laid, they must be removed from
the enclosure or the egg-laying box. Eggs are part of the diet of
most monitors and they will be consumed quite readily by
adults or destroyed during digging activities. In reptile eggs, the
embryo attaches to a disk at the top of the egg and adheres via
a membrane to maintain its position within the egg. In bird
eggs, however, the embryo is held in position via a sinew, which
allows the egg to be rotated during incubation. Monitor eggs
must be kept oriented along a single plane and not rotated. Eggs
can be marked on the upper (dorsal) surface with a graphite pen-
cil to show the plane of orientation. A pen should not be used
to mark eggs, as some types of ink contain toxic substances that
can be fatal to the embryo. When marked, the eggs can be
placed into a prepared box that is used for incubation. This box
should contain either vermiculite or perlite mixed with an equiv-
alent weight of water. Varanus mertensi eggs can tolerate a huge
range in humidity or water potential, and this ranges from a 2:1
to a 5:1 ratio of water to substrate (Eidenmüller and Wicker
1998). The particle size of either substrate is not significant.
During incubation, the temperature should be between 26.5 °C
and 29.5 °C, with humidity between 80% and 90%. If the
water uptake of an egg is too high, the embryo inside can

An appropriate nest box for a small ground-dwelling monitor.

Freckled Monitor (Varanus tristis orientalis) hatching.

Gould’s Monitor (Varanus gouldii flavirufus) hatching in a perlite incu-
bation medium.



become stressed by the water pressure and die. A small indenta-
tion of the egg is not a concern, provided that the eggshell is
white. If more water is added to the substrate, this will be
absorbed by the egg and plump up any indentations, especially
if this occurs early in the incubation process. Be careful not to
drop water onto the surface of the egg, as this may harm the
development of the embryo. Generally, the incubation period
correlates with the adult size of each species, but it may also
depend on the temperature and humidity during incubation.
Incubation is a process that requires a great deal of patience,
because the incubation periods in the literature can be different
than the incubation period that you experience, even for the
same species. If hatchlings are overdue and the eggs still appear
viable, do not open the egg. In most cases, the egg will be
opened too early and reveal a premature hatchling, which is
unlikely to survive.

If the humidity in the egg-incubation box is high it some-
times becomes apparent that eggs have swollen and in some cases
there is water exuded from the egg. This is called “sweating.” If
one or more eggs start to sweat during incubation, carefully slit
the egg on the upper side. This slit in the egg decreases the pres-
sure on the embryo and may enhance its chances of survival.

Rearing Hatchlings
After hatching, each individual should be measured and weighed
carefully. These data may be of interest to other breeders. Special
care should be taken to avoid injuring the young animals, especially
when trying to weigh and measure them. They likely will be intent
on escape and even seemingly innocuous movements in the hand
can damage a young varanid. After measuring the hatchlings, they
should be placed in a cage where they can be reared. The size of the
enclosure should be sufficient for the animals to move about their
new quarters with ease. The cage should not, however, be so large
that you do not have sufficient control over the food items being
presented to the new arrivals. This will prevent insects that escape
the hatchlings from becoming hidden in some recess of the cage,

reappearing at night when the hatchling is asleep, and presenting
a physical risk to its survival. The furnishings within a hatchling
enclosure should be much the same as those of the adults, although
they may be somewhat smaller. Care must be taken to ensure that
cork bark and stones are securely positioned so that they cannot fall
and crush the hatchlings. A small bowl of fresh water should always
be available.

Hatchlings of most monitor species can be kept together
in small groups. Exceptions to this are V. storri (Eidenmüller
and Horn 1985) and V. prasinus, which should always be raised
separately. Young V. storri have fatally injured each other
through constant biting, and the only way to avoid this is by
keeping them separately. Other species also may exhibit aggres-
sion toward one another, so I suggest keeping a close eye on all
groups of hatchlings until a determination that they are com-
patible is justified. The problem of stress can be quite pro-
nounced in V. p. beccarii; hatchlings in some instances have
been known to refuse food and die within hours (Eidenmüller

250 IGUANA  •  VOLUME 12, NUMBER 4  •  DECEMBER 2005 EIDENMÜLLER

Hatchling Emerald Tree Monitors (Varanus prasinus) must be raised
individually.

Mertens’s Water Monitor (Varanus mertensi) hatching.



IGUANA  •  VOLUME 12, NUMBER 4  •  DECEMBER 2005 251MONITORS

1996, Eidenmüller and Wicker 1991). Most other monitor
species are not problematic in this respect. When rearing a
group of hatchlings, close attention should be paid to the feed-
ing behavior of all individuals to ensure that they are all obtain-
ing sufficient food. As they grow, some animals will become
dominant and exclude others from the food. These animals
should be removed.

During the first two to ten days, the small monitors still live
on yolk, which is the last thing to be incorporated into the body
cavity before hatching. This food source for a newly hatched
varanid can last between hours and days depending on the health
of the female, size of yolk in the egg, and metabolic rate of the
hatchling. Hatchlings should be offered food items that are small
enough for them to overpower, such as small crickets or cock-
roaches. Food animals should always be treated with a vitamin
and mineral powder. Freshly caught grasshoppers are an excellent
addition to the diet of a captive monitor as they contain more
vitamins and fiber than cultivated insects. Be certain to avoid
catching insects from agricultural land, beside freeways, or in
some gardens, where they are likely to have been subjected to pes-
ticide and herbicide applications. Many of these applications may
be harmful to your hatchling. Cultivated crickets and locusts are
fed a biased diet that may not have all the necessary vitamin and
mineral components to ensure the long-term health of your
monitors. Several manufacturers sell gut-loading cricket diets that
considerably improve the nutritional value of food insects.

References
Auffenberg, W. 1988. Gray’s Monitor Lizard. University of Florida Press,

Gainesville.

Bayless, M.K. 1992. African varanids: Diets in captivity and in the wild.
Varanews 2(5):2–3.

Dedlmar, A. 1994. Haltung und Nachzucht des Smaragdvarans (Varanus
(Odatria) prasinus). Salamandra 30:234–240.

Eidenmüller, B. 1996. Keeping and breeding the Aru Black Tree Monitor
Varanus beccarii (Doria, 1874). Reptiles 4(12):76–83.

Eidenmüller, B. and H.-G. Horn. 1985. Eigene Nachzuchten und der gegen-
wärtige Stand der Nachzucht von Varanus (Odatria) storri Mertens, 1966.
Salamandra 21:55–61.

Eidenmüller, B. and R. Wicker. 1991. Einige Beobachtungen bei der Pflege
und Nachzucht von Varanus (Odatria) timorensis similis Mertens, 1958.
Salamandra 27:187–193.

Eidenmüller, B. and R. Wicker 1992. Varanus (Odatria) prasinus beccarii
(Doria, 1874), Pflege und Zucht. Salamandra 28:171–178.

Eidenmüller, B. and R. Wicker. 1998. Beobachtungen an Varanus mertensi-
Gelegen, inkubiert unter verschiedene Bedingungen. Herpetofauna
20:30–34.

Gaulke, M. and E. Curio. 2001. A new monitor lizard from Panay Island,
Philippines. SPIXIANA 24:275–286.

James C.D., J.B. Losos, and D.R. King. 1992. Reproductive biology and diets
of goannas (Reptilia: Varanidae) from Australia. J. Herpetol. 26:128–136.

Lenz, S. 1995. Zur Biologie und Ökologie des Nilwarans, Varanus niloticus
(Linnaeus, 1766) in Gambia, Westafrika. Mertensiella 5:1–256.

Losos, J.B. and H.W. Greene. 1988. Ecological and evolutionary implications
of diet in monitor lizards. Biol. J. Linn. Soc. 35:379–407.

Pianka, E.R. 1968. Notes on the biology of Varanus eremius. W. Austral. Nat.
11:39–44.

Pianka, E.R. 1969. Habitat specificity, speciation and species density in
Australian desert lizards. Ecology 50:498–502.

Pianka, E.R. 1969. Notes on the biology of Varanus caudolineatus and Varanus
gilleni. W. Austral. Nat. 11:76–82.

Pianka, E.R. 1970. Notes on Varanus brevicauda. W. Austral. Nat.11:113–116.

Pianka, E.R. 1970. Notes on the biology of Varanus gouldii flavirufus. W.
Austral. Nat. 11:141–144.

Pianka, E.R. 1970. Notes on the biology of Varanus tristis. W. Austral. Nat.
11:180–183.

Pianka, E.R. 1982. Observations on the ecology of Varanus in the Great
Victoria Desert. W. Austral. Nat. 15(2):1–8.

Shine, R. 1986. Food habits, habitats and reproductive biology of four sym-
patric species of varanid lizards in tropical Australia. Herpetologica
12:346–360.

Sprackland, R.G., Jr. 1993. Rediscovery of a Solomon Islands Monitor Lizard
(Varanus indicus spinulosus) Mertens, 1941. Vivarium 4(5):25–27.

Ziegler, T. and W. Böhme. 1996. Über das Beutespektrum von Varanus dumer-
ilii (Schlegel, 1839). Salamandra 32:203–210.

Hatchling Pilbara Monitor (Varanus pilbarensis) in the terrarium.

Monitors
Natural History, Captive
Care and Breeding
By Bernd Eidenmüller
174 pages (ful color), hardcover
132 color photos, 46 drawings 
distribution maps for each species
Price: 39 EUR
www.herpeton-verlag.de
ISBN 3-936180-13-X

Expected Release: January/February 2006
Available at: Breck@Herplit.com

All presently recognized monitor species are covered in this
book.

Contents: Name and Systematics, Distribution and
Zoogeography, Captive Care, Reproduction, Raising the
hatchlings, detailed descriptions of each varanid species
and more ...

Author Bernd Eidenmüller has extensive experience suc-
cessfully keeping and breeding many species of monitors.
His primary interest has been the smaller members of the
genus, particularly those from the Indo-Australian region.

The author has produced countless popular and scientific
articles adding significantly to our scientific knowledge of
these animals, even discovering an entirely new species! 




