The Gila Monster
Heloderma suspectum (pronounced Hee'-la) is one of only two species of
venomous lizards, its cousin the Mexican Beaded Lizard being the other.
With its generally sluggish behavior and benign disposition, it nonetheless
must be treated with caution. It can bite quickly and hold on tenaciously.
The bite of Heloderma suspectum, while not considered lethal, is very painful
and should be considered a medical emergency.
Rather than injecting venom
through hollow fangs like venomous snakes, Gilas have enlarged, grooved
teeth in their lower jaw. When they bite, their powerful jaws chew the
venom in through capillary action along the grooves in these teeth. Gila
monster venom is about as toxic as that of a western diamondback rattlesnake.
However, a relatively small amount of venom in introduced in a Gila bite.
On an interesting
note, a component of Gila monster venom called Exendin-4 is currently being
investigated as a promising new drug to treat type 2 diabetes. This peptide
stimulates the secretion of insulin in the presence of elevated blood glucose
levels. It also has the effect of slowing gastric emptying. Phase I clinical
studies have recently begun with this exciting investigational drug.
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
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
Gila monsters spend most
of their lives hidden below the ground. This is responsible for the limited
information we have about them. There are three things that make them particularly
well suited for the harsh environment in which they live.
First, they are large lizards
(the largest in the U.S.) measuring to about 22 inches in total length
and are able to store more energy than smaller lizards. They store fat
in their tail and in their bodies. Second, they are capable of eating relatively
large meals. They have been observed in the wild eating meals up to one
third of their body weight. Third, Gilas have low resting metabolic rates.
Their low metabolic rates,
and the ability to eat large meals, combined with their large capacity
to store fat, make frequent searching for food unnecessary. Therefore,
they are rarely seen above ground. It has been suggested that Gilas can
consume their entire yearly energy budget in three or four large meals.
Most of their above ground
activity occurs in 3 months in the spring. Not only is this when mating
occurs, but it is when their main source of food (vertebrate nests) is
most abundant. They are mainly diurnal (active during the day) with activity
occurring mainly in the morning.
Gila monsters have a home
range of about one square mile. They are usually solitary animals, but
do gather in communal areas in the spring for mating.