Region III Quarterly

Volume 3 - No. 2

April, 1941


By Earl Jackson,
Montezuma Castle National Monument.

Of all the wild creatures that live in the United States, there is none more completely shrouded in ignorance and superstition than the Gila Monster (Heloderma suspectum). For this he has largely to thank his secretive habits, his ugly and fearsome appearance, and the fact that he belongs to that universally feared group, the reptiles. If you would care to investigate with me some of the fact and fancy connected with these animals, perhaps together we can erase some of those erroneous beliefs.

The Gila Monster belongs to the lizard family known as Helodormatidae. This family is very significant, for it contains the only poisonous lizards to be found on the face of the earth. It has only one genus, Heloderma, and two species, Suspectum and Horridum. Suspectum is the only poisonous lizard occurring in the United States, and derives part of its popular name from the fact that its principal range is along the Gila River of southern Arizona and its tributaries. It is essentially a creature of the desert, rarely found above 4,000 feet altitude, although the range extends from northern Sonora to as far as southeastern Nevada and southwestern Utah, and from southwestern New Mexico on the east to the California line on the west.

Helodorma horridum, the "Beaded Monster" of Mexico, is a semi-tropical creature, living principally along the Pacific Coast from Sinaloa in the north to the peninsula of Tehuantopec in the south, being quite abundant in this range. It also extends into central Mexico and southward to the northern states of Central America. Oddly enough, while the two lizards are very similar in structure and habits, they are separated by a wide area of land in which neither is found.

Arizona Gila Monster
ARIZONA GILA MONSTER. A. W. Carson photo, Flagstaff, Arizona.

The Gila Monster has a very stocky body and a heavy club-like tail. An adult averages between 16 and 19 inches long, although occasionally they reach 22 inches, and rarely 24. The head is massive, flat on top, and shaped somewhat like a triangle with a little of the front tip cut off to make a blunt end. Bulging jaw muscles behind the eyes add extra width. The front part of the head is purplish brown to black, as are the feet and the lower parts of the legs. The rest of the body is made up of this same color varied with irregular rings and blotches shading anywhere from a creamy white to a reddish orange. In some cases the dark predominates; in others, the lighter color. The markings, while quite irregular, tend toward the tail to become fairly clear transverse bands. The markings continue underneath the body; although here they are less complex. After the shedding of skin, which occurs at different times through the year, the pattern is fresher looking than at other times. The lizard is sometimes called "an animated bead bag", for it is covered on the top and sides with raised tubercles, on beads. The scales of the under body by contrast are true scales; they are quite smooth and square, and touch each other, overlapping slightly.

Heloderma horridum, the Gila Monster's Mexican relative, commonly called "El Escorpion", averages a little larger in size. A normal adult will be slightly over 20 inches long, an unusual one, 24 inches. A rare one is sometimes recorded nearly 30 inches long. Hornidum is built the same as Suspectum, but the body color is a little different. The head is usually entirely black or dark brown, and this color prodominates over the rest of the body, some specimens being almost entirely black. The contrasting color blotches are a rich yellow.

The Gila Monster has stocky and powerful legs and feet, with strong sharp claws, which it uses occasionally to climb into low bushes and up steep places, the heavy tail being used as a support. The feet are interesting, for their internal structure is almost exactly like that of the human hand, having the same number of bones, with a similar arrangement and shape. When you meet the reptile in his native state, it is easy to understand how his weird shape and coloring, and the vicious looking head, make him an awesome sight. As he walks over the desert with long and deliberate steps, which throw the body into graceful flowing curves, the large black tongue darts frequently in and out. This wicked looking forked tongue adds to the fear-inspiring picture, although it is completely harmless. When the creature is annoyed or disturbed he is apt to lift his head slowly and open his mouth to a menacing attitude. Then he makes an impressive blowing noise, accomplished by forcefully ejecting bursts of air from his lungs.

The monster looks tough, and he is tough. I received a freshly killed specimen and proceeded to inject it hypodermically with an alcoholic preservative. Imagine my surprise when I found it almost impossible to force the sharp needle point through the skin! It is no wonder the lizard is safe from sharp thorns and cactus spines. The tenacity to life is so remarkable that it is extremely difficult to kill one. The tough skin, the heavy build, and the fat insulation, all work for its protection, But, like other reptiles, it will soon die if left in the direct sunlight of a hot summer day. The body has no heat regulating mechanism, hence its temperature is within a degree or two of the environment. When you think that a fever of 10 degrees will kill a human, you can imagine what happens to a reptile on sun-baked earth when the thermometer even in the shade hovers at 110 or 115 degrees.

One of the remarkable features about the monster is the heavy musculature in the jaws and mouth. These powerful jaw muscles, combined with a bulldog disposition to hold on, mean that when he grabs hold of something in anger it is very difficult to get free. He bites with such vigor that even if the body is severed from the head, the set jaws retain their grip. Dave Gorsuch, in the Arizona Magazine for June, 1937, described the case of a small dog which suffered a broken foreleg as the result of an encounter with a Gila Monster. While the bite was probably not strong enough to crush the bone, the struggles of the dog for freedom from the vise-like grip broke the leg. In contrast with jaw and mouth muscles come very inadequate muscles for the throat, which is literally just a wide hollow tube. The throat has so little muscle tissue that the lizard has to raise his head and swallow mainly by gravity. If a specimen which has just fed is picked up by the tail and hung head downward, the feed falls out.

It is well known that Mother Nature is a bit capricious in running her desert cafeteria. Sometimes there is plenty of food, and at other times there is scarcely a thing to be found. The monster is prepared for these variable spells. When food is ample he eats prodigiously, converting it into fat which he stores in his tail. When food is scarce, he can live for many months on this accumulated energy. Slow metabolism is, then, a secret to successful life on the desert. You can immediately spot a well fed individual by the girth of his tail, or a poorly fed or sickly one by the reduced diameter of it.

Two common misunderstandings about Gila Monsters can be readily dismissed. One is that the creature has no anal opening, and therefore is poisonous because of accumulation of decaying waste in the system. The other is that the breath is poisonous. The reptile has a perfectly normal reptilian alimentary canal and anal opening, as dissection and observations have established beyond the shadow of any doubt. The breath, while disagreeable and fetid, is certainly not more dangerous than the exhalation from the mouth of any creature which will eat spoiled or rotten food. Part of the halitosis might be traced to the appetite for eggs, no matter how ripe.

In scanning the life cycle of the Gila Monster one finds there are gaps in the story. This means that more research is necessary before we can speak with confidence about all their habits. Nesting traits, however, are pretty well known. In southern Arizona the female usually hunts a nest location in the latter part of July. She finds a moist sandy area, preferably near a stream; it must have a sunny exposure, so that the sand will be warmed by the sun's heat. If the sand is too dry the eggs won't hatch; if it is too damp, they spoil. She digs a hole four or five inches deep, and lays six to ten eggs at varying intervals. This done, she scrapes the sand back into the hole, entirely covering it, and then goes away and forgets the place.

The eggs when laid are about two and one-half inches long, and contain small but well-formed embryos. The shell is a white oval with a rough surface, thin and soft, but not fragile. After 28 to 30 days of incubation the three and one-half inch youngsters dig their way to the surface, where they greet the light of day fully equipped, even to pugnacious disposition, to fend for themselves. They are skinny creatures, unlike the well fed parent, but have their permanent coloration. The young monsters have prodigious appetites, but grow slowly. O. N. Arrington, Tucson, Arizona, authority, finds that at the end of a year one is still skinny and underweight, not over six and one-half inches long and weighing less than an ounce and one-half. This is in contrast to the average adult weight of 20 ounces. It was impossible to learn from the available literature just when the lizard reaches sexual maturity. If it is like many other large reptiles in this respect, the female would lay in the summer of her third year. Also, more by inference than anything else, I feel certain that mating occurs early in the season, in March or early April. Scanty evidence suggests that they mate and forget each other.

The monsters are seen most frequently in the spring, when they are quite active hunting mates and food. With the hot weather of May and the following summer months they are rarely seen in sunlight. They hide in shaded spots during the heat of day, and prowl at night. The casual observer sometimes concludes, because they are seldom seen in summer, that they aestivate during the hot dry season. However, a herpetologist can find the reptiles all year, except in late autumn and winter, he knows their hot weather preference for evening and night hours, and that even at best they are hard to see in their native habitat, so ho chooses his hunting hours when most people are at supper or in bed. Howard K. Gloyd, Director of the Museum, Chicago Academy of Sciences, was able to collect a few in July, August, and early September. He obtained them in late evening after sundown. Two were captured just after a heavy thunder shower.

Little is known about the natural foods of Gila Monsters. In captivity they prefer eggs to anything else, but will eat them mixed with chopped meat or corn meal. One will push an unbroken egg against a corner until it cracks, then push the smooth tip of the tongue in side and lap up the contents. A hungry individual may eat three or four chicken eggs at a meal. Charles T. Vorhies, Economic Zoologist, University of Arizona, found that one will occasionally swallow a freshly dead mouse if the mouse is placed in the jaws. He found an unidentified small furry mammal in the stomach of one. Another specimen was reported to him as containing three newly born jackrabbits.

On two occasions, Mr. Arrington, the Tucson authority, saw the reptiles gorging themselves on eggs from quail nests. He states that experimental attempts to feed them on a variety of insects met with failure. His belief is that normally they eat a few small animals, but mainly the eggs of other reptiles and ground birds. Their taste for water should not be overlooked. They like it, although they are awkward about taking it. They have to drink by inserting the nose in the fluid, then raising the head to allow the water to slide down the throat. In closing the comment about food, we owe the monster an explanation. In no sense is his taste for quail eggs a major menace to the birds. At best, the reptile is not numerous, and in the long run he takes only a small percentage of the eggs. He is simply one of the many predators which keep the quail population stable. Kill off such predators, and the prolific quail would abound in such numbers they would starve.

Perhaps the most controversial point about the Gila Monster is that of whether he is poisonous, and if so, to what extent. To answer this question let us first take a brief anatomical look at the mouth. It is equipped with both upper and lower sets of toeth, all of which are grooved, both in front and in back. The front groove is the deeper, and is formed by projecting folds of enamel. The teeth, when extracted and dried, are found to be hollow inside, but there is no means for poison to be conveyed within them. All the teeth are rather small and fragile, being easily broken. While the mature tooth are fastened to the bone, the young teeth are free and easily detachable. Teeth are shed periodically, and replacements occur in the fairly wide spaces between the other teeth. The four anterior teeth of each side, both upper and lower, are larger than the others, deeper grooved, and slightly longer, with faintly back curving tips. They protrude above the gums a little more than an eighth of an inch. In biting, the monster frequently leaves no teeth wounds, or if present, they may be very slight. This is because several of the fragile teeth may be broken off as the powerful jaws clamp together on the victim, and because some may be absent due to shedding.

The Gila Monster quite definitely produces a poison. It can be separated and dried into crystals which look much like those of dried rattlesnake venom. As a venom producing creature, however, he is rather low in the scale of evolution. Herpetologists point out that originally there were no poisonous reptiles. Gradually the saliva of some of them began to secrete mildly poisonous elements, until eventually in many cases a specialized function of part of the saliva glands became that of venom production. This development continued until, as in the rattlesnakes, the poison glands became quite separate and distinct from those which continued to make saliva. On the other hand, the monster still secretes poison more or less as a sideline in a saliva gland. As another case in point, his shallowly grooved teeth represent but a beginning of what, in the rattlesnake, became a teeth in which the groove folded over and closed, leaving a hollow fang like a hypodermic needle. Also, the monster lacks a direct connection between the gland and the tooth, whereas the rattlesnake poison sac attaches by a duct to the base of the fang.

The monster produces its venom from two large glands, one on each side of the lower jaw or mandible. Each gland is divided into four primary subdivisions or lobes, which increase in size from front to back. Each lobe is a structurally independent organ, and opens by a separate canal or duct leading through the wide mandibular bone to terminate between the anterior teeth and the lip. Each of these lower teeth is like a flower in a pot. It stands by itself, its base completely surrounded by a cup-shaped fold of mucous membrane. Immediately external to the cup is a shallow groove, limited at the outer side by a prominent fold of mucous membrane intervening between lip and lower jaw. This groove is divided into a series of shallow depressions by transverse bands of tissue which connect its outer membrane border with the jaw, attaching between the teeth. The ducts of the glands open into the more anterior of these shallow depressions. The depressions undoubtedly serve as temporary reservoirs for the secretion, and the tips of the upper teeth fit into them when the mouth is closed. So we find, in short, that the poison producing glands, located only in the lower jaw, each have four separate and distinct openings which release poison-carrying saliva not directly into or against the four front teeth on each lower side, but in pools near them.

A review of the literature that has been written on Gila Monsters during the past 58 years reveals considerable difference of opinion about their danger to man. So far as I am able to determine, published case records of bites fail, in any single instance, to sinew the bite; as the direct primary cause of death. Most authorities admit, however, that a sufficiently large injection of the poison might kill a healthy adult. That no such person has reportedly died from the venom might be explained by stating several variable factors: (1) Frequently the reptile has few or no teeth at the time of biting, hence could open no avenue for the poison to enter the system. (2) The teeth are short, securing little penetration at best. (3) The open groove is a very inefficient venom carrier. (4) Sometimes only the upper teeth penetrate the flesh, and since they carry only the poison which adheres to them from contact with saliva from the lower jaw, little can enter the wound. (5) Even the lower teeth have no direct connection with the poison carrying ducts. (6) Poison is usually highly diluted with saliva by the time entry is effected. (7) Age, size, and condition of the reptile determine its quantity of venom. Some specimens would have comparatively little.

It should be further pointed out that in many cases of painful and serious bite the poison may have played a lesser role than was imagined, because: (1) the nature of the reptile, once it bites a victim, is to clamp its very powerful jaws as tightly as it can and then, without loosening its grip, to lacerate the flesh with a sub-biting motion. So you got the natural bruising effect and shock from a powerful animal's bite, as well as torn flesh. (2) Since the mouth of the creature is a filthy germ-laden space, and since a lacerated flesh is a perfect spot for infection, serious contamination can enter the wound and combine with even a small amount of venom to produce possibly disastrous results.

In short, we are wise to consider the Gila Monster as a dangerously poisonous reptile. In all cases of bite, one should completely sterilize the wound as promptly as he can, and in serious cases use a tourniquet and the incision and suction method as prescribed in first aid treatment of snake bite. Fortunately, the monster is usually so placid he doesn't get mad enough to bite. But when pne is seemingly tranquil and lying quite motionless, especially if he has been teased, liberties should not be taken with him. If you reach a hand close to him he can swing his head like lightning to one side to seize the hand. A sorely aggravated individual can pivot his whole forebody on his hind legs for a quick lunge.

Man is about the only creature the reptile has to fear. Even the rattlesnake has no terror for him. The Tucson authority, Mr. Arrington, describes what happens when one is placed in a cage with a rattler. The snake acts afraid, and crawls off to the other side of the cage. The monster follows in a menacing attitude, and when within striking range makes a quick sideward thrust of its head to imprison the snake's body in its jaws. Characteristically, it hangs on like a bulldog. The snake writhes and lunges, seldom attempting to strike. Striking does no good anyway, for the fangs can't penetrate the tough hide. In three to five minutes the snake is usually dead. You can't help having a lot of respect for our tough skinned neighbor of the desert, but you have nothing to fear from him if you let him alone. Like some people, he is a bad one to "monkey" with, but a good one to get along with.

When you suddenly encounter a Gila Monster in his native haunts, and he looks at you in surprise for a moment before deciding to retreat, his bearing is that of a king. With his nearly black head reared well above the rest of his mottled body, and his broad chest elevated above the ground on wide spaced and sturdy legs, you find his pose has suggested to you, not that of a "cold and crawly" creature, but that of one of Nature's noblest animals, the African lion.

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Date: 17-Nov-2005