Mexican Vine Snakes – just mildly venomous

Willson photo of vine snake

The Mexican vine snake (Oxybelis aeneus), aka Brown vine snake, is a very slender snake that typically gets three to six feet long. It has a pointed snout and the head length is about three to four times its width. They are masters of camouflage. The Arizona-Sonora Desert Museum has a small one on exhibit in the reptile room. Click here to see a photo of a large one taken in Santa Cruz County, Arizona.

Mexican vine snakeVine snakes are usually gray to brown on the upper side and have yellowish undersides. The snout is elongated and the mouth can open very wide. This snake is active during the day and often hunts in trees. Its main prey are lizards, frogs, and birds.

The vine snake is a mildly venomous, rear-fanged snake, but it is not considered dangerous to humans. However, a bite can cause an itching sensation. When threatened it will often hold its mouth open widely exposing the dark lining of the oral cavity and throat (see third photo here). Also when threatened, it sometimes releases foul smelling secretions from its vent. Farting is a defense.

According to Arizona Game & Fish, the vine snake lays a clutch of 3-5 eggs in late spring to early summer in an underground burrow or den. Incubation lasts about 2.5 months.

According to a paper, Van Devender et Al,, Factors Influencing the Distribution of the Neotropical Vine Snake (Oxybelis Aeneus) In Arizona and Sonora, Mexico :

“In southern Arizona and northern Sonora, the neotropical vine snake (Oxybelis aeneus) lives in temperate oak woodland, canyon riparian woodland, desert-grassland, and pine-oak woodland communities at 1160 to 1650 m [3800 to 5400 feet] elevation. Perennial plants in an oak woodland habitat in the Atascosa Mountains in the center of the Arizona distribution of the species, have strong biogeographical affinities with the grasslands and woodlands of the southwestern United States and the northern Sierra Madre Occidental in Mexico. The plant communities are wholly different in vegetation structure and only 2.2% of the Atascosa site perennials reach tropical lowlands near Alamos in southern Sonora. The restricted area occupied by 0. aeneus in southern Arizona is characterized by relatively mild winter temperature and relatively high annual precipitation that falls mainly as summer monsoon rain. The northerly limit of O:xybelis in southern Arizona is apparently limited by winter freezing above 1650 m and by summer aridity below 1160 m. The northward range limit is associated with final failure of tropically-evolved morphology. physiological tolerances, and behavior under continental physiographic-climatic constraints.” (Read full paper)

According to the Tucson Herpetological Society vine snakes sleep in loose coils in trees and shrubs at least six feet off the ground. “They have been observed from March into November in our area, although most are found during the summer rainy season. The vast majority of records are for the Pajarito-Atascosa Mountain range complex, from about Walker Canyon east to Arivaca Lake and Ruby. A specimen was collected in 1968 from ‘near Washington Camp’ in the Patagonia Mountains. There are at least four unconfirmed (no photos or specimens) reports from the western flank of the Santa Rita Mountains (Montosa Canyon and Agua Caliente Cave), and a similarly unconfirmed report from Thomas Canyon on the eastern slope of the Baboquivari Mountains.”

[Credit: the “head-on” photo above was taken by Dr. John Willson, now Assistant Professor Department of Biological Sciences, University of Arkansas, who kindly gave me his permission to use the photo. The photo was taken in Costa Rica.]

More snakes and lizards:

Arizona Coral Snakes – pretty and very venomous

Clever Horned Lizard

The Coachwhip a colorful snake

Desert Tortoise

Gopher snakes

Kingsnakes versus Rattlesnakes

Metachromatic spiny lizards


Speckled Rattlesnakes

Spinytail Iguanas

Venomous Lizards









Spinytail Iguanas stalk the Arizona-Sonora Desert Museum

Among the may animals you may encounter during a visit to Tucson’s Arizona-Sonora Desert Museum are some big lizards, the Spinytail Iguanas.

Spinytail Iguana adult

There are several species of spinytail iguanas (genus Ctenosaura) native to Mexico and Central America that are found in desert scrub and forest. The lizards range from 10 inches to over 39 inches long (some sources claim five feet long). Several species have been introduced into the U.S. in Arizona, Texas, Florida and perhaps other places.

These lizards were introduced into the Arizona-Sonora Desert Museum(ASDM) in the 1970s. They are reproducing but apparently have not expanded beyond Museum grounds, at least none have been reported off the grounds. Maybe, if any leave the Museum they quickly fall prey to coyotes, bobcats, and hawks. The adult lizards at ASDM can get up to about two feet long.

Thomas C. Brennan, proprietor of says that the “lizards that exist at the Arizona-Sonora Desert Museum are a genetic cross between Ctenosaura conspicuosa (San Esteban Island Spiny-tailed Iguana) and C. hemilopha macrolopha (Sonoran Spiny-tailed Iguana).”

While these lizards have the run of the Museum, the easiest place to see them is in the Mountain Habitat and the Bighorn Sheep habitat. These lizards are territorial and usually don’t run away from you. They are rather feisty. While they usually stand their ground, they can run at up to 20 mph. Adults can inflict a painful bite.

The lizards are omnivorous and eat a variety of plant material, bugs, other lizards, small mice, birds and eggs. They take shelter in crevices and tree hollows.

“Mating generally occurs in the spring. Males show dominance and interest by head bobbing, eventually chasing the female until he can catch her and subdue her. Within eight to ten weeks, the female will dig a nest and lay clutches of up to 30 eggs. The eggs hatch in 90 days with the hatchlings digging their way out of the sand. These juveniles are typically green with brown markings, although all brown hatchlings have been recorded as well.” [source]

Newly hatched spinytails at ASDM are bright green, about six inches long. They prefer to climb in trees and bushes. The green gradually disappears as it blends into the grays and browns of the adult lizards.

Spinytail Iguarna juvenile

The young adult in the third photo, just a foot off the path, posed as many people took his photograph. He did watch us warily. This one is about 18 inches long.

Spinytail iguana young adult

According to Wikipedia: “In some parts of Central America, the black spiny-tailed iguana is farmed alongside the green iguana as a food source and for export for the pet trade. Although it is heavily hunted it does not appear to be endangered in any of its native territory.

According to the World Association of Zoos and Aquariums (WAZA): “These iguanas live in colonies, ruled by a pecking order: One male in the colony is dominant, and although the other males hold territories, they will only defend them against one another and not against the dominant individual. Territorial displays involve color changes, body inflation, jaw-gaping, ‘push-ups’ or rapid nodding of the head, and sometimes, biting and tail thrashing battles. Larger males usually hold bigger and better territories and they mate more often. Combat often occurs when iguanas are attaining or defending a territory or a mate. The males always court, but they can only progress if the partner provides them with the right stimuli. The female must respond by species specific sexual stimuli. She must also signal that she is receptive-with mature ova ready for fertilization. The males often bite, scratch, or lick females that have signaled their receptivity.”

Head out to the Arizona-Sonora Desert Museum to see if you can spot the big guys and the babies.

In recent years, there was some concern among Museum staff about having a non-native species on the grounds. The Museum considered removing them from the grounds. I asked Craig Ivanyi, executive director of ASDM about this. Here is what he said:

These lizards “naturally occur in the Sonoran Desert, but not in Arizona. Transplants from Sonora (& Isla San Esteban), Mexico, were apparently released in the 1970’s. We’ve done studies to better understand population demographics and species behavior on the Museum grounds, as well as to see if there’s any evidence of them leaving our property and establishing themselves elsewhere. In spite of not seeing any evidence of them establishing themselves elsewhere, the decision was made several years ago to reduce their numbers on grounds and, over time, to create a sterilized population so that it naturally dies out some day. To this end, we have been opportunistically sterilizing individuals, as well as collecting and sending them to other zoos for exhibit elsewhere.” I am told by another ASDM scientist that this program is essentially defunct.

See also:

Kingsnakes versus Rattlesnakes

Gopher snakes

Clever Horned Lizard

Metachromatic spiny lizards


Speckled Rattlesnakes

Venomous Lizards

Kingsnakes versus Rattlesnakes

Kingsnakes eat rattlesnakes, hence their name. Apparently kingsnakes are either immune to or tolerant of rattlesnake venom. Kingsnakes also eat other snakes, lizards, amphibians, birds and bird eggs, and rodents.

Rattlesnakes can identify kingsnakes by smell. Rattlesnakes usually retreat in presence of a kingsnake and hold their head and tail close to the ground while arching their back and attempt to hit the kingsnake. Watch a 3-minute Discovery Channel video of a common kingsnake attacking and eating a rattlesnake:

Kingsnakes are usually docile, but when disturbed, they may hiss, vibrate their tail, and strike. If seized by a predator such as a coyote, the kingsnake can expel a noxious musk.

Kingsnakes come in a great variety of patterns and colors. There is some controversy over names and how many varieties there are. This is made more confusing because some varieties can interbreed with other varieties. I use the Arizona-Sonora Desert Museum naming convention here. Most kingsnake adults are three to six feet long. Below are photos of the most common varieties in the southwest. All kingsnakes have smooth scales unlike the ridged scales of the gopher snake. All kingsnakes are powerful constrictors.

Desert Kingsnake

Kingsnake desert

This black and white (or cream) is the most common kingsnake in the Tucson area. It is native to Arizona, New Mexico, and Texas. It normally grows to four feet but some are over six feet long. This kingsnake normally mates from March through June and produces up to 12 eggs that incubate for 60 days. Hatchlings are 8- to 10 inches long.

Common Kingsnake

Kingsnake common

The common kingsnake used to be called the California kingsnake. It has alternating brown/black and white/cream to yellow colored bands. Adults range from 2.5 to 6 feet long. This snake occurs throughout most of Arizona, California, and Baja California. Normal mating time is May through August. The females produce as many as 24 eggs which hatch in 60 days. Hatchlings are 6- to 8 inches long and are more brightly colored than the parents.

Sonoran Kingsnake

Kingsnake Sonoran

The Sonoran kingsnake is usually deep chocolate brown which may look black in some lighting conditions. It occurs in southern Arizona and in Mexico south to Sinaloa. Young snakes may have spots of white or yellow under their chin. This snake is commonly 3- to 4 feet long and rather plump compared to other kingsnakes.

Mountain Kingsnake

Kingsnake Arizona Mtn

This pretty snake is variously called the Arizona Mountain kingsnake or Sonoran Mountain kingsnake, It may be 2.5 to 4 feet long. This snake inhabits the Sierra Madre in Sonora and several mountain ranges in southern Arizona. I have seen this snake in the Bradshaw Mountains near Jerome. Some occur also in Utah and Nevada. It may be confused with the coral snake, but it is much larger. Remember the rhyme: “Red touch black, OK Jack.” These snakes breed in spring and generally produce four to nine eggs.

Milk snake

Kingsnake Sinaloan Milksnake

On this snake, the red bands are much wider than the black and white/yellow bands. It, too, can be confused with the coral snake. The rest of the rhyme: “Red touch yellow, kill a fellow.” In kingsnakes, the red band is surrounded by black bands.

The milk snake is commonly 1.5- to 4.5 feet long. It occurs mainly in southern Sonora, but there have been some specimens collected near the Little Colorado River in northern Arizona. This snake occurs mainly in forests and is mainly nocturnal. Breeding is similar to the mountain kingsnake.

I handle snakes at the Arizona-Sonora Desert Museum including all the kingsnakes shown above. Kingsnakes are my favorite snake. They seem more curious than other snakes. When I’m holding a snake and someone comes near, the kingsnake will take a look and flick its tongue to get a taste. Taste, by the way, is the snake’s most important sense. Their forked tongue picks up particles in the air which are analyzed by the Jacobson’s organ in the roof of the mouth. The organ is so sensitive that it can distinguish differences from each side of the forked tongue. This gives the snake a sense of direction for where the taste is coming from.

Kingsnakes have many pointy teeth to grip their prey. In the photo below, notice that snakes have four rows of teeth on top. Notice also that the teeth are very small. I have never been bitten, but other Docents have been. They say it is no big deal because the teeth are so small.

 Snake teeth

Besides the western kingsnakes described above, several species, mainly black varieties, live in the mid-western and eastern states. The eastern kingsnakes eat copperheads as well as rattlesnakes.

Be kind to kingsnakes you find in your yard. They will help protect you from rattlesnakes and eat rodents.

See also:

Gopher snakes
Clever Horned Lizard
Metachromatic spiny lizards
Speckled Rattlesnakes
Venomous Lizards (Gila monster, Beaded lizard)

Metachromatic Spiny Lizards

The spiny lizards are medium to large lizards up to 10 inches long (including tail).  They have keeled, pointed scales that are usually a subdued gray or tan, a wide purple stripe down the back and scattered turquoise scales mixed with tan and brown on the back and sides.  They also have a dark collar under and around the neck.

These lizards exhibit metachromatism which means they change color depending on the temperature: generally with darker colors in cool temperatures.  They also change color with the seasons.

The first photo shows a male in all his splendor during mating season with his blue belly and throat.


During mating season, the female develops a red, pink, or orange head.  The second photo shows a female just beginning to develop the color.   By the way, this particular female liked to climb on the rocks near my back porch.   She became quite tame and I could hand feed her June Bugs.  I kept in mind that lizards have many sharp teeth.


There are actually two species of spiny lizards common here: the Desert spiny lizard (Sceloporus magister) and the Clark spiny lizard (Sceloporus clarkii).  I cannot tell them apart with confidence.  I think, however, the Clark tends to have darker bands on it legs.  Both species are primarily insect eaters.

The Desert Spiny occurs in six western states including almost all of Arizona, east to Texas and south to Sinaloa, Mexico; it is found from sea level to 5000 feet.

The Clark Spiny is found in central to southeastern Arizona, southwestern New Mexico, and south to northern Jalisco, Mexico, from sea level to around 6000 feet.

Both species are found mainly in desertscrub and thornscrub, among rocks.   The Clark Spiny prefers trees, but is also found in rocky areas and may be found in oak woodlands and tropical deciduous forest and oak-pine forest in Chihuahua, Mexico.

The third photo shows a male on the left and female on the right.  Notice that the female is missing her tail.


Many lizards have expendable tails that can be sacrificed to a predator if necessary.  The wiggling detached tail will distract the predator and allow the lizard to escape.  The ability to shed a tail is made possible by tiny fracture planes in the vertebrae which allows it to break easily.  The lizard can help the split with muscular contractions when a predator grabs the tail.  Blood vessels constrict quickly to minimize blood loss.  The tail can regenerate over several weeks, but it is usually smaller and lighter colored.  There is no bone regeneration; the new tail is supported by cartilage.  If the original tail was only partly detached, a new one grows anyway and you may see a double or triple-tailed lizard.

The spiny lizards lay four to twenty four eggs in the summer into early fall which take 60 to 75 days to hatch.  The lizards grow out of their skins, and usually shed in patches rather than in one piece like a snake.  The spiny lizards eat insects, other lizards, and some plant material such as leaves, berries, and flowers.  They are preyed upon by snakes, coyotes, and birds of prey.

If you see one of these lizards, it may display by doing push-ups.  This allows the lizard to get a better look at you, and it is also meant to intimidate you by making the lizard look bigger.

Craig Ivanyi, executive director of the Arizona-Sonora Desert Museum, tells a story about a lizard encounter:

Meeting One’s Match

Collared lizards can be quite pugnacious. In fact we had a male in one of our enclosures that routinely visited all other similar-sized lizards, just to make sure they knew exactly who was in charge.

When we introduced a male desert spiny lizard to this enclosure, the collared lizard quickly ran over to assert himself. However once he was within a few inches of the spiny lizard he seemed to realize how large this newcomer was. The two lizards took positions next to each other, bodies parallel, then sized up one another with sidelong glances. Eventually they took off in opposite directions. Apparently neither felt superior enough to press the issue.