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Gila monster

Heloderma suspectum


by Rhodri Phillips


Identification: Gila monsters are a species of lizard found in Mexico and the deserts of Southern America. Its name originates from its discovery and abundance in the Gila River basin that crosses Arizona and passes through the Mexico border. The species can be easily distinguished from other reptiles by its flat body and striking pink/orange and black colouration. But this colouration also serves another purpose, it’s a clear signal to predators of the hidden capabilities the species has to defend itself. Gila monsters are one of the few venomous lizards in the world, producing a potent cocktail in their salvia glands that enters wounds inflicted by its strong jaw. Unfortunately, this ability has led to the species being villainized by humans, with a number of tales talking about this “deadly” species. However, only one human fatality has been reported in the last 100 years as caused by this species unfairly labelled as a monster.


© Rhodri Phillips


Life cycle: Gila monsters are largely solitary by nature, living in burrows they create between rocky outcrops in their preferred desert grassland habitat. Interestingly the species has been shown to change its activity to match the temperatures of the surroundings, becoming nocturnal if the ambient temperatures become too hot. Their burrows also offer refuge during winter, in which the cold-blooded species hibernate using fat stored in their tail to survive.


Once spring arrives the following year Gila monsters emerge and begin bulking up for the breeding season which starts in the early summer. Despite their slow speed and poor eyesight, males of the species engage in a heated fights to impress nearby females. However, unlike other species they do not fight to the death or even in most cases cause injury. Instead the individuals appear to enter a wrestling match of sorts, where the strongest individual wins a fair fight by pinning the smaller male to the ground, often wrapping their tails around each other for leverage.

After mating the females of the species will lay a single large clutch of eggs, placing them in a shallow hole and covering them with soil. The eggs themselves are incubated by the heat of the desert sun, hatching around 4 months later. The juveniles of the species receive no parenting and appear to hatch with the knowledge and ability to hunt from day one. Although while young their diet is primarily made from insects and bird eggs, but can include a number of small mammals. Similarly to snakes, Gila’s swallow their prey whole, digesting it over several hours.


Image byDavid Mark from Pixabay


Species Importance: As a desert predator the Gila monster plays a vital part in its ecosystem. With plant life often at a premium the over grazing of plants can be a serious issue, intensifying the desertification process and making areas even harder for species to live in. By being a generalist predator that often eats the eggs or young of herbivorous species like rabbits, Gila monsters help prevent this intensification while also being a food source themselves to birds of prey and coyotes. The true importance of the species likely lies in its slow speed and inability to actively hunt. It means that as a species they are unlikely to kill healthy adults, allowing the natural process of evolution to carry on.


Photo by David Clode on Unsplash


Conservation status: Currently designated as near threatened by the IUCN, populations of the Gila monster have been declining in recent years. An estimated decline of 30% has been seen across US populations, however detailed information on the species is not available. This is in part due to the mostly solitary nature of the species, although it has been found in around 100 surveys throughout its range.

The biggest threats to the species are habitat loss and urbanisation, with many of the populations declines in America being attributed to new constructions in New Mexico. A population increase in the towns near the Gila’s monsters’ range has displaced individuals, while an increase in farming is further squeezing the species by limiting suitable egg laying areas. New highways are for the increasing populations are further increasing mortality rates as collisions with vehicles have been increasingly common. However, for the most part it is still thought the population is stable. Its presence in a number of protected areas should ensure the species survives into the future, even if some populations are lost.


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