The Gila Monster is a lizard many of us have seen before, whether it be in a book or in a nature documentary on TV. They are hard to mistake, with their striking orange and black colouring and their beaded reptilian skin. One of the main reasons why the Gila Monster gets so much attention throughout the world is the fact that it is one of only two venomous lizards in the world, the other being the Beaded Lizard, Heloderma horridum. There are two subspecies of Gila Monster, the Reticulate Gila Monster, H. s. suspectum and the Banded Gila Monster, H. s. cinctum. The Reticulate Gila Monster lives in the southern region of the Gila Monster’s range, while the Banded Gila Monster is a northern subspecies occurring primarily in the Mojave Desert. The Reticulate Gila Monster tends to have its lighter markings broken up by dark scales, giving it a reticulated pattern, while the Banded Gila Monster generally has more unbroken bands of lighter scales.

Gila Monsters can reach lengths of 60cm and have thick, forked tongues that are similar to that of a monitor lizard. Gilas have thick robust tails that are specifically adapted to allow them to store fat away as an energy reserve during times where there is little food around. Although the Gila Monster’s venom is very potent, they are only prone to bite when they are attacked or threatened. Their venom is delivered by grooves in the animal’s teeth, and therefore they need to chew on their prey items in order to ‘move’ the venom into their prey. In the more than 150 years that Gila Monsters have been known to science, there has not been one recorded fatality from a Gila Monster bite. The Gila Monster produces venom in modified salivary glands in its lower jaw, unlike snakes, whose venom is produced in the upper jaw. The Gila Monster lacks the ability to forcibly inject the venom; instead, the venom is propelled from the gland to the tooth by chewing. Capillary action brings the venom out of the tooth and into the victim. The teeth are loosely anchored, which allows them to be broken off and replaced throughout life. Gila Monsters have been observed to flip over while biting the victim, presumably to aid the flow of the venom into the wound. Because the Gila Monster’s prey consists mainly of eggs, small animals, and otherwise “helpless” prey, it is thought that the Gila Monster’s venom evolved for defensive rather than for hunting use. A defensive use would explain the Gila Monster’s bright warning coloration.

Although the venom is a neurotoxin, as toxic as that of a Coral Snake, the Gila Monster produces only small amounts of it. The Gila Monster can bite quickly, especially by swinging its head sideways, and it can hold on tenaciously and painfully. Symptoms of the bite include excruciating pain, oedema (swelling caused by fluid in the body’s tissues), and weakness associated with a rapid drop in blood pressure.

Although your Gila Monster can appear very calm and docile in captivity, never become too complacent as a bite from an adult is extremely painful. As Gilas do not have hollow fangs like venomous snakes they can be safely handled with a pair of heavy leather gloves.

Since these animals are so unique and rare, they are protected in their natural habitat, and therefore anybody trying to capture or sell wild specimens will suffer severe penalties. Fortunately due to this any specimens that are offered for sale will be captive bred by a breeder, which is what every breeder wants.

Gila Monsters are diurnal animals, which in their natural habitat are most active during springtime when there is an abundance of food. In the wild they will feed on bird eggs and tortoise eggs and also occasionally feed on small mammals like baby rabbits.

Gila Monster by Gary Nafis
Gila Monster by Gary Nafis


Captive Care
Gila Monsters are considered hardy and undemanding captives that are best housed in individual cages, which allows for easier feeding. That being said, many breeders have also had success housing them in a colony setup, although animals are separated during feeding times. The minimum dimensions for an individual Gila Monster enclosure is around 120cm x 60cm x 60cm, although a bit bigger is often better. As a substrate you can either use playground sand, bark chips, newspaper, or a naturalistic substrate. Just keep in mind that they love to dig, so a sandy substrate is always ideal for them and will keep things interesting. Temperature should be regulated at 24 – 27°C at the cool end and around 29 – 32°C at the warm. As the Gila Monster is diurnal it is important that you provide them with a natural light cycle; in winter the light cycle can be about 8 hours of light and 16 hours of darkness, which can then be increased through the year until in summer you can have 14 hours of light and 10 hours of darkness. Mice and rats of the appropriate size are a good food choice for captive Gilas, and you can offer mature males a mouse once every two weeks and breeding females can be offered a meal twice a week. Be careful as Gilas have a good appetite and a slow metabolism and can easily become obese. Obesity can cause health issues and will also affect the ability to reproduce successfully. It has been said that you should be feeding domestic chicken eggs or chicks and rather just feed rodents. Breeders suggest that Gilas can thrive without any special UVB lighting and many breeders keep them in large racking systems in plastic tubs similar to that of a Ball Python. Make sure to also provide a large sturdy water bowl that cannot be easily tipped over. If the bowl is large enough it is not uncommon for Gilas to spend a significant amount of time soaking in it.

The first challenge a keeper is faced with when breeding Gila Monsters is the fact that there is no physical way of determining the sex of a Gila Monster. In mature specimens there is a general rule that males have broader heads where females have a narrow heads and a pear shaped body. These are general trends though and is therefore not 100% accurate when determining sex. The only accurate way of determining sex is by ultrasound, where in males the testes are clearly visible and the females’ follicles are also visible.

One of the most important aspects to ensure successful breeding is your female’s diet. She has very specific feeding requirements as egg production has uses a lot of energy for a female Gila. If a female Gila does not have adequate fat reserves she will not reproduce.

In order to stimulate reproduction a cooling period is required. This period consists of 3 months at temperatures of 13 to 14°C. It is important that all feeding is stopped for at least two weeks before cooling in order to make allow them to fully digest their last meal. Temperatures are slowly reduced over two weeks until final temperatures are reached. Then after the 3 months the temperatures are slowly returned to normal. No food is offered during this cooling period and only water is provided.

Care must be taken that no two male Gila Monsters are placed in the same cage, especially during breeding season, as one may get injured due to not being able to escape from the other in captivity. Some breeders intentionally place two males together in order to compete and when one male retreats they then separate them and introduce them to the female. They do this in order to stimulate the males to breed. Although this is practiced by some breeders, Gilas will breed successfully without male combat, and hence it seems unnecessary to combat them and risk one of your males getting injured. From the cooling period it generally takes about 4 – 6 weeks for the adults to become receptive to mating. At this time you can start placing the females into the males’ cages where mating will then occur.

A few weeks before females are ready to lay they will become very active and start digging around the cage. At this time it is important to provide an egg-laying box, which can contain damp sphagnum moss. Make sure it is only slightly damp and not too wet and maintain a temperature of around 28°C in the nest box. The time from a successful mating to laying ranges from 42 – 55 days and Gilas have been known to lay anywhere from 2 – 13 eggs.

Recommended temperatures for incubating Gila Monster eggs is 25 – 26.5°C. At these temperatures, and if all goes well, eggs should hatch after about 124 to 150 days. Eggs should be incubated in a container that with slightly damp vermiculite. Unlike snake eggs Gila Monster eggs are more sensitive to moisture and should be incubated in vermiculite that is mixed with water at a 1:4 ratio. That means for every 100 grams of water you add 400 grams of vermiculite!

Gila Monsters are still very rare in captivity in South Africa. Specimens are mainly found in reptile parks and zoos for display. Hopefully in the near future we will see some private breeders being able to acquire the correct permits in order to keep and breed these amazing lizards in private collections in South Africa!

Gila Monster - up close
Gila Monster – up close


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