Official Web Site of the City of Phoenix

  Range:

• Mojave and Sonoran deserts of southeastern California.
  
• Extreme west part of Texas
  
• Southern Nevada to Puebla, near the southern edge of the Mexican plateau.

Description
The Mohave Rattlesnake is a medium sized rattlesnake Adults can reach lengths of 2 to 4 feet. Well defined light-edged diamonds down the middle of their back. The tail has contrasting light and dark rings. The white rings are much wider than the black rings. Some Mohave Rattlesnakes are greenish, but can be colored greenish gray, or olive green, or occasionally brownish or yellowish.

Food & Hunting

• The Mohave Rattlesnake eats kangaroo rats, lizards and other rodents. They are ambush predators.
  

Habitat
The Mohave Rattlesnake is primarily nocturnal, hiding under crevice or in burrows during the hot day. Habitat may vary from the dry desert to the grasslands and bushes. Most commonly found in scattered scrubby growth like creosote bush and mesquite.

• Most active from April to September
  
• Hibernate alone or in small groups during the winter months
  
• They will vigorously defend themselves when disturbed.

Breeding

Deterrence/Prevention:

• Never handle a rattlesnake, even if it is believed to be dead. Serious, even fatal, envenomations have been documented to occur after handling the decapitated head of a rattlesnake up to 90 minutes after it was severed.
• Do not reach or step into places outdoors that are not visible.
• At home, remove debris in which snakes might hide (eg, log piles). Remove items, such as bird feeders, that might attract snakes—seeds that fall from bird feeders attract rodents, which attract snakes.
• Heavy clothing (such as hiking boots) may retard some strikes.
• Young children should be closely supervised, and older children should be educated to avoid snakes.
• Keep garage doors closed to prevent rattlesnakes from seeking shelter in garages.

• Scientists have identified 36 rattlesnake species.
• Rattlesnakes live in only North and South America.
• 13 species live in Arizona, more than any other state.
• Rattlesnakes use the “loreal pit”, a heat-sensing organ between the nostril and eye. to locate pray and potential predators
• These snakes have glands that make venom, much like saliva glands make saliva.
• The rattle is made of keratin, the same material found in human hair and fingernails.
• The age of a rattlesnake cannot be determined by counting the segments of it’s rattle.
• Rattlesnake prey may include small mammals, birds, reptiles, amphibians, and centipedes.
• According to Arizona Poison Centers, less than 1% of rattlesnake bites result in human deaths.

Order: Squamata
Family: Helodermatidae (venomous beaded lizards)
Spanish name: escorpión

 The Gila monster is a large, heavy- bodied lizard reaching a little over 1¼ feet in length. The head is large, with small, beady eyes; the tail is short and fat. The family name Helodermatidae means “warty skin,” referring to the beaded look of the dorsal scales, due to the presence of osteoderms (small bones) under the scales. The lizard is bright pink and black, usually in a reticulated pattern, but in a banded pattern in some populations.

The bulk of this lizard’s range is in western and southern Arizona, continuing to southern Sonora, Mexico, but it can also be found in extreme southeastern California, southern Nevada, extreme southwestern Utah, and southwestern New Mexico.

The Gila monster is most commonly found in mountain foothills dominated by saguaros and palo verde trees. It also uses washes that extend down into valleys. It may use burrows dug by other animals, or construct burrows of its own.

Gila monsters prey on newborn rodents, rabbits, and hares, though ground nesting birds and lizards, as well as eggs from birds, lizards, snakes and tortoises are also eaten. Young Gila monsters may consume as much as 50 percent of their body weight in one feeding, while adults are capable of consuming 35 percent of their body weight in a single feeding. They are active mainly during the day from March through November, and may be seen basking at the entrances to their shelters in winter and early spring. Hibernation takes place from the end of November through February. Some sources estimate they spend up to 98 percent of their time in their subterranean shelters. Generally an animal occupies two burrows over the course of a year, one from autumn through early spring and another during the warmer spring and summer months. The latter burrow is usually in or near a bajada, while a higher elevation, foothill burrow is used when cooler temperatures arrive. Little is known about reproduction in the wild. An average of 5 eggs, but as many as 12, may be laid in late summer. In southern Arizona, Gila monsters breed in May and June, with eggs laid in late June through mid August. The eggs incubate and develop from fall to early spring; young appear the following April through June. There is no other known egg-laying lizard in North America where eggs over-winter and hatch the following year.

Gila monsters are one of only two venomous lizards known to occur in the world. The other, the Beaded Lizard (Heloderma horridum), is found in southern Sonora and further south in thornscrub and tropical deciduous forest.

Venom is produced in glands in the lower jaw and expressed along grooved teeth as the animal bites. Once the lizard bites, it generally holds on and chews more of the venom into its victim. Though the bite is rarely life-threatening to humans, it may cause pain, edema, bleeding, nausea and vomiting. A Gila monster’s venom is believed to be a defensive weapon. The animal probably does not need venom to subdue its defenseless prey and the intense pain caused by the venom readily causes a predator to change its mind. Before biting, the lizard will hiss, gape, and back away from its would-be attacker. If these efforts fail, it will bite with amazing speed. Gila monsters should not be handled!

Reptiles, especially venomous ones, are often poorly understood and greatly feared. With the Gila monster this combination has led to misinformation and the generation of many myths. Interesting but untrue are stories about how the Gila monster is venomous because it lacks an anus and “all that stuff went bad in there.” Or about how “once they bite down, they can’t let go until sundown,” or “if one bites you, don’t worry, it has to turn upside down to get the venom in you.” In 1952 the Gila monster became the first venomous animal in North America to be afforded legal protection; it is therefore illegal to collect, kill, or sell them in Arizona. Though it is an animal with a fairly large range, it has a spotty distribution primarily clumped around mountain ranges.

Beaded Lizard


Beaded lizzard hatchlings

Besides the Gila Monster, The Mexican Beaded Lizard is a venomous lizard. The Beaded Lizard’s skin consists of several tiny beads called ostioderms. Each bead contains a tiny piece of bone that gives them almost an armor plated skin.

The lifespan of these lizards is between 30 and 50 years. Female average adult size is 30 inches and weight three and a half to five pounds. Male average adult size is 36 inches and weight five to six pounds.

Most Beaded Lizards reach sexual maturity at two and a half to three years old. Once oviposition occurs, the incubation period is around 165 to 215 days. At about that time the hatchlings will pip their head out of the egg. It usually takes two or three days for them to come all the way out, absorbing their yolk sack and ingesting the liquid content of their egg. Newly hatched neonates are usually five to six inches and weigh around 40 grams. Until the animals are substantial in size, sexing is nearly impossible. Males generally have much broader heads and longer necks, with females having narrower heads and shorter necks.

The animals originate in the Pacific Drainages from Southern Sonora, Mexico to Southwestern Guatemala and two Atlantic drainages, from Central Chiapas, Mexico to Southeastern Guatemala. Habitat is primarily tropical deciduous forest and thorn scrub forest, also found in pine-oak forest, with elevations from sea level to 1500 meters. In the wild, the animals are only active from April to mid-November. They spend only about an hour per day above the ground, and their natural diet is consistent of reptile and bird eggs and occasionally small mammals. As with the Gila Monster, this lizard uses its venom primarily as a defensive weapon. (Johnson, J. P. and C. Ivanyi, 2001. North American Regional Beaded Lizard Studbook. 3rd Edition. Arizona-Sonora Desert Museum.)

To the left: A tooth of a Heloderma horridum, notice the pit in the tooth.
To the right: The Jaw of a Gila Monster (Similar to a Beaded Lizard)
Both drawings come from Bogart and Del Campo's The Gila Monster and Its Allies

(Photos & reference information courtesy of Desert USA)


back to top

Back to Critters

Back to SMEEC