Gila
Monster
By: http://www.drseward.com/
and
Psyco
S.C
Handling
Although a Gila bite
is not life threatening, it should be considered a medical emergency and should
obviously be avoided. If proper care and judgment is exercised, a bite is
something that never needs to happen.
The bite of a Gila
monster won’t kill you, but will make you wish you were dead! It is very
painful. The biggest threat of a bite comes from the fact that the typical adult
Gila is a very calm and docile animal—it would be very easy to become complacent
handling them. Never put yourself in a position where a bite could occur, no
matter how much trust and familiarity you have with your animals. Perhaps the
general calm nature of adult Gilas in captivity is related to the fact that they
have few if any regular predators in the wild.
Gilas of all sizes
can safely be handled using a pair of heavy leather gloves. Since Gilas don’t
have the hollow fangs of front-fanged venomous snakes, even if their teeth could
penetrate the leather, most of the venom would be absorbed by the glove.
Experienced Gila keepers frequently handle them without the aid of gloves. With
proper experience and care this can be done safely. They are gently, but
securely grasped around the neck in a way to restrict the lateral movement of
their head. Their body weight can then be supported with the other hand. Gilas
are very strong animals and are capable of quick and powerful lateral biting
movements—a careful and secure grip is important. I recommend that all handling
of your Gilas be accomplished wearing appropriate leather gloves as
protection.
Just as the typical
adult Gila is a calm and docile animal, the typical young Gila is quite snappy.
I would call it more defensive than aggressive. This is perhaps due to the fact
that small Gilas are easier prey to a number of predators than are their adult
counterparts. Due to their small size and attitude, hatchling and young Gilas
are more difficult to handle. Not only are they more likely to bite, but in a
six inch lizard the part you grab is much closer to the part that bites! Even
so, they can very easily be handled with the before mentioned
gloves.
I recommend that Gilas not be
regularly handled except for husbandry needs. This is both for safety reasons as
well as for the welfare of the animals.
Feeding
One of the pleasures of working
with Gilas in captivity is their almost universal fondness for readily available
foods, namely mice and rats. The typical Gila will eat whenever food is placed
before it. In fact, they will easily eat to the point of obesity. Weight gain is
also facilitated by a naturally low metabolic rate. Avoid obesity—an
obese Gila is not a reproductively fit Gila.
Gilas are easily maintained on a diet of mice or
young rats (freshly killed or frozen-thawed). Feeding eggs to Gilas should be
avoided (a mouse can be dipped in pasteurized egg whites to entice the rare
reluctant feeder to eat).
Frequency of feeding will depend on the
individual animal and the time of year. For a maintenance diet I feed adult
males about every two weeks. In preparation for egg laying and to recover from
egg laying, I feed females twice a week. Gila Monsters have unusually low
metabolic rates, and will eat until they become obese if allowed to do
so.
Fresh water should be provided in a bowl that is
not easily tipped over. If a large enough bowl is provided, it is not unusual
for Gilas to spend long periods of time soaking. If they are allowed to do so,
the water bowl will need daily cleaning. I prefer to provide water in a
disposable 16 ounce deli container
Caging
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Gila Monsters make hardy,
undemanding captives. Adult Gilas can be maintained in
aquariums, large plastic containers (e.g., Rubbermaid 65 quart clear
boxes), or custom cages. Adults should have a minimum of 3-1/2 square feet
of floor space. In the wild, Gilas spend most of their lives inactive and
underground, so large amounts of space are not required. The cage should
be large enough to provide a good thermal gradient—warm on one end and
cool on the other Some people maintain Gilas in groups in
larger cages. However, individual housing facilitates feeding and
maintenance. In the wild, Gilas are usually solitary animals except when
they congregate in the spring for mating. |
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Cage substrate can be as
simple as newspaper or wood shavings. I use Sani-Chips®, a chipped aspen
bedding product. It is inexpensive and very easy to spot clean. In
addition to regular spot cleaning , it is a simple matter to totally
replace the bedding periodically In order to create a temperature gradient
and allow the animal to thermoregulate, under cage heating (such as
Flexwatt® heat tape) should be provided for a portion of the cage and
controlled with a thermostat or a dimmer switch. Maintain a temperature of
85 to 90 degrees Fahrenheit measured on the substrate over the heat
source. For animals preparing for the breeding season, a good range of
temperatures is critical. I prefer a larger range of temperatures, from
the low to mid-70’s F on the cool end to the low 90’s F on the hot
end. |
Hibernation
In many vertebrates, including
reptiles, after breeding there is a "refractoriness" to light and temperature
stimulation. In other words, under conditions of light or temperature that would
normally stimulate the reproductive system no stimulation occurs. A period of
short days or cold temperatures is required to break this refractoriness and
regain sensitivity to the conditions of light or temperature that will stimulate
the reproductive system. In Gila monsters, this can be accomplished by holding
them at cold and dark conditions in the winter.
Most recommendations involve a
three-month cooling period with temperatures in the mid 50’s. Hibernation is
begun by slowly decreasing the temperature until the final cooling temperature
is reached.
With my breeding colony
I suspend feeding at least two weeks prior to cooling. This allows the Gilas to
fully digest their last meal before winter cooling. Beginning the first of
December, my animals are slowly cooled and then maintained at a temperature of
53-57 F. On the first of March, the temperatures are slowly returned to normal.
I don’t believe it is critical how slowly the temperatures are
changed.
Water should be
available during hibernation both for drinking and to increase the humidity of
their hibernating environment. Provide it in a container that can’t be easily
tipped over. I feel it is important to provide adequate humidity during
hibernation to prevent dehydration of the animals.
Mating
Many individuals have recommended
keeping multiple males and females together in a group during breeding season.
This is both because of the difficulty in determining sex as well as the thought
that combat between males will facilitate successful breeding. It is the opinion
of the author that this approach can be counterproductive to success.
In the wild, Gilas demonstrate a
structured social system including establishment of dominance through male-male
combat. The hypothesis is that in free-ranging Gilas as well as in other
squamate reptiles, the “winner” of these male-male fights gains access to
females. However, in the typical captive group setting the dynamics of the
male-male interactions are very different from what occurs in free-ranging
Gilas. In a typical captive setup, males lack an avenue for escape. Dominant
males will often fight one another incessantly at the exclusion of all other
activities, including mating. Male combat can be a useful tool to stimulate a
reluctant male to breed, but it must be managed carefully to be successful in
the captive environment.
Gilas will breed successfully without
male combat. I house the Gilas separately and simply introduce females into the
male’s cage individually usually without any male-male pairing. Individual
housing of the Gilas also facilitates their husbandry.
Animals are paired beginning the
first week in April and copulation is typically observed by the middle of April
(4-6 weeks after emergence from hibernation). Multiple females can be rotated
through the cage of one male leaving each female in for several days. I will
usually breed a given female several times.
Copulation has been observed to last from 15 minutes to
as long as 2.5 hours.
Oviposition
Once a female is gravid, she
should be separated from her cage-mates if she is not already alone. This will
prevent unnecessary stress to her and will prevent cage-mates from eating her
eggs.
Through close observation one can
observe distinct changes in the behavior of a female from copulation to
oviposition. The first stage is marked by behavior that I characterize as "quiet
but alert". She will spend long periods of time motionless but very alert,
frequently basking in a warm part of the cage. A couple of weeks before
oviposition, she will become very active, digging about the cage. By this time
she should be provided with a nest box. I use damp sphagnum moss as an
egg-laying medium. A short time before oviposition, the gravid female will
retire to this nest box and remain relatively inactive.
Prior to egg laying the female
provides an adequate environment for the developing eggs assuming she has an
opportunity to thermoregulate. It is important to provide an environment in the
nest box that will be supportive to the developing eggs, also. This means
appropriate moisture and temperature. I am careful not to keep the egg-laying
medium too wet, spraying at least daily to maintain slight uniform moisture.
Keep the temperature in the nest box the same as the incubation temperature
(about 79 degrees F).
A normal, healthy clutch of
fertile eggs is usually laid over a period of several hours. Eggs that are laid
over longer periods of time (sometimes over several days) are more likely to be
infertile or non-viable.
Time from successful mating to
oviposition appears to be 42-55 days. Gilas have been known to lay from 2-13
eggs, the number being somewhat proportional to the size of the
female.
You may see eggs that were not
fertilized. Infertile eggs may appear smaller and more yellow than fertile eggs
and will not be as turgid (they may appear "deflated"). Some infertile eggs will
look every bit as good as a fertile egg from the outside. However, on candling
there is no sign of a blood ring and they look more opaque on the inside
(fertile eggs appear translucent when candled).
There are several possible
explanations for infertile eggs. One possibility is the female was not
inseminated at the optimal time. Another explanation is a problem with the
viability of the male’s sperm. Perhaps he did not have access to appropriate
temperatures earlier in the season and his sperm was unable to development
properly.
Incubation
A lot of conflicting information
has been published regarding the incubation of Gila eggs and many breeders have
had difficulties bringing eggs to full term. It is important to consider three
factors that affect the environment of the developing Gilas. These factors are
temperature, moisture and oxygen tension.
Suggested temperatures for
incubating Gila eggs range from 79-85 F. It has been suggested that incubating
them over 85 degrees F can result in failures.
I incubate the eggs at 77-80
F—never over 80 F.
Most breeders use vermiculite as
an incubating medium, although other substrates have been used. Suggested
water-vermiculite ratios range from 1:1 to 1:4 (by weight). I am of the opinion
that excessively wet incubation medium is harmful to Gila eggs and is
responsible for many failures.
Although Gila eggs should not be
exposed to excessive contact moisture, they do need to be exposed to adequate
humidity.
In the past, eggs were set up in
a relatively dry mix of vermiculite. I would carefully weigh the water and
vermiculite to create a ratio of 1:4. The eggs were half buried in the
vermiculite with the embryo on the top. Setting up the eggs with the embryo on
top allowed me to more easily monitor the growth of the developing
Gilas.
With my previous incubation
setup, maintaining the proper moisture required the addition of water to the
vermiculite many times during the incubation period. I was careful to add water
of the same temperature as the incubator to prevent thermal shock to the
developing embryos (this was done by keeping a water bottle in the incubator at
all times). The humidity in the incubation chamber as well as the amount of
ventilation to the incubator and the individual egg containers would affect the
rate of water loss. The egg containers were periodically weighed to determine
water loss and water was added to compensate. I weighed each container weekly
until I got a sense of how much water was lost how frequently. I was careful to
not place water directly on the eggs as this has been suggested to contribute to
egg death. Eggs exposed to inadequate amounts of moisture will begin to dent. I
would occasionally remove the eggs from the incubation medium and remix the
substrate to maintain an even distribution of the
moisture.
This technique was successful at
hatching Gila eggs, but also had it’s problems. It was difficult to maintain
stable conditions for the developing eggs. The frequent tinkering required to
maintain appropriate moisture levels over the entire four and a half months of
incubation was no less than a real pain. For several years I have been
experimenting with alternate techniques to incubate Gila monster eggs. I wanted
to develop a technique that fulfilled certain criteria. The primary and most
obvious goal in creating the new protocol was to create an environment ideally
suited to the development of Gila eggs. Equally important, though, was to create
a stable environment that needed little attention during the long period of
incubation. Additionally, I wanted a technique that was easily reproducible; I
wanted anyone to be able to use the technique with success equal to my
own.
After many years of trying
different materials and different procedures, I have come up with a technique
that I believe fulfills all these requirements. I call it the Hygroscopic
Incubation Technique
Hatching
If all goes well, after about 124 to 150 days of
incubation a young Gila will arch its head back within the egg and, with several
biting motions, slice through the egg membrane and shell with its egg tooth.
After pipping, young Gilas will frequently take a few days before emerging from
their eggs. During this time they will absorb the considerable remaining yolk
into their abdomen. Do not remove the Gilas prematurely.
Once Gilas pip, they will begin to drink the
liquid contents of their egg. If you are lucky and you peer into the slit in the
egg you may observe the Gilas tongue go in and out as it takes its first drink.
Even after exiting the egg, hatchling Gilas will return to the shell and consume
all that remains within it. This is likely an adaptation to living in a harsh
and arid environment.
It is best to leave
hatchling Gilas alone and let them pip and exit the egg naturally. A normal and
fully developed baby Gila should have no trouble exiting its egg without any
assistance. If you "help" by enlarging the slits in the shell or if you open the
egg prematurely, the Gila may, in turn, exit the egg prematurely—before all the
yolk has been absorbed. Contain your excitement leave them alone to hatch
naturally!
How to aquire
Gila monsters do not make good “pets”. However, they can
be ideal captives for the serious herp enthusiast. In fact, many of the
characteristics that make them ideally suited for their environmental niche,
also make them well suited for the captive environment. They generally make
undemanding captives.
Gilas are protected throughout their range and cannot
legally be taken from the wild. There are, however, animals being removed from
the wild illegally that show up in the trade. Avoid acquiring any animal unless
you have proof that it is legally captive bred. Not only will you avoid the
potential legal implications of dealing with poached animals, but also you will
increase your chance of successful propagation—captive bred Gilas are more
likely to breed in captivity than animals taken from the
wild.
There are several reputable sources for captive-bred Gila
monsters. I always recommend acquiring hatchlings and raising them yourself.
That way you can be more certain of the origin of the animals, you have complete
control over their environment, and you are not inheriting someone else’s
failures. The main disadvantage, if your intent is to breed them, is waiting 2 ˝
years or longer for them to become sexually mature.
You can be successful breeding Gilas with only a single
pair. However, you increase your chances for success significantly with a larger
group. I consider a group of about eight animals to be a good-sized breeding
group.
Range
The Gila Monster Heloderma
suspectum occurs from extreme southwest Utah to southern Sonora and northern
Sinaloa; extreme southwest New Mexico to southern Nevada and just into
California.
The northern subspecies is the Banded Gila Monster
H. s. cinctum and the southern subspecies is the Reticulated Gila Monster
H. s. suspectum.
Heloderma suspectum occurs up to an
elevation of 1500 meters. It has been observed to be more common in the wetter,
rockier paloverde-sequaro desert scrub association than the drier, sandier
creosote bush-bersage association. Heloderma suspectum also seem to
prefer rocky foothills and avoid open flats and agricultural
areas
Morphology
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The Gila monster is the largest lizard
native to the United States. They are a stout lizard with an elongated
body, short limbs and thick tail. A large adult is 20-21 inches in total
length. Hatchling are generally six to six and one-half inches in
length.
The dorsal coloration of the Gila monster
is contrasted black with pink or orange. In the southern subspecies, the
Reticulated Gila Monster, the light markings are broken up to form a
reticulated pattern. In the northern subspecies, the Banded Gila Monster,
the light markings generally form an unbroken band across the back. There
is extensive variation in the appearance of Gila monsters throughout their
range. At times there is not a clear distinction between the two
subspecies based on body pattern. There are individual animals well within
the range of the banded Gila monster that have the broken up appearance of
a reticulated Gila and visa versa. Gila Monsters of both subspecies are
similarly patterned when they hatch—they both have a distinctly banded
appearance . As they mature, the differences in pattern develop. This is
referred to as ontogenic change. | ||
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