Fans of the fantastic website Heloderma.net already know how knowledgeable and passionate Dr. Schwandt is about Gila monsters, and in September 2019 he released his long-awaited book on our favorite subject. Being the Gila geek I am, my order was placed the day pre-orders were announced and was certainly not disappointed when it arrived. The book covers a wide range of topics in detail and covers some information not previously seen in other books. Certainly a must-have for your collection of Heloderma reading, the book can be purchased from the author on his website or here.
The Yahoo! Heloderma group created and maintained by Mark Miller is being taken down. So, I thought it would be a shame to let Mark’s work fade into oblivion and have posted his well-curated Heloderma Bibliography here for posterity. One of these days I will update this list with some of the newer books that have come out since it was compiled.
CREATED by Mark Miller / UPDATED circa 1998 by Mark Miller
Allen, Morrow J. 1933. Report on a collection of Amphibians and reptiles from Sonora, Mexico, with the description of a new lizard. Occas. Papers Mus. Zool. Univ. Michigan, no. 259, pp.1-15
Arnberger, L. P. 1948. Gila monster swallows quail eggs whole. Herpetologica, vol. 4, pp. 209-210
Beddard, Frank E. 1906. On the vascular system of Heloderma, with notes on that of the monitors and crocodiles. Proc. Zool. Soc. London 1906:601-625, 8 fig.
Bloyd, Gary R. 1970. The gila monster (Heloderma suspectum). Bull. Florissant Herpetol. Soc. (8):1-2.
Bogert, Charles M., and Rafael Martin del Campo. 1952. Geoclines and ontoclines in lizards of the genus Heloderma. Annu. Meet. Amer. Soc. Ichthyol. Herpetol. 32nd., Austin, Texas.
Bogert, Charles M., and Rafael Martin del Campo. 1956. The Gila Monster and its allies: the relationships, habits, and behavior of the lizards of the Family Helodermatidae. Bull. Amer. Mus. Natur. Hist. 109:1-238, 35 fig., 20 pl., 5 tab., 2 Maps.
Boulenger, Georges Albert. 1891. The anatomy of Heloderma. Nature (London) 44:444.
Boulenger, Georges Albert. 1891. Notes on the osteology of Heloderma horridum and H. suspectum, with remarks on the systematics position of the Helodermatidae and on the Vertebrae of the Lacertilia. Proc. Zool. Soc. London 1891:109-118.
Boulenger, Georges Albert. 1918. Les lezards Helodermatides de l’Eocene Superieur de la France. Comp. Rend. Acad. Sci. (Paris) D 166:889-893.
Cheek, L.W. Watch Out! The Little Monsters Bite. Arizona Highways 1990 Vol. 88 (8): 42-46
Cooper, Robert H. 1969. Melanoma in Heloderma suspectum Cope. Proc. Indiana Acad. Sci. 78:466-467.
Cuesta Terron, Carlos. 1934. El escorpion. Heloderma horridum Wiegmann. 2a Ed. revisada por Rafel Martin del Campo. pp. 1-14. Folletos Divulgacion Client., Inst. Biol., Univ. Nac. Mexico.
Curtis, L. 1949. Notes on the eggs of Heloderma horridum. Herpetologica 5(6):148.
Dolensek, E.P., Cook, R.A. Clinical Challenge [Radiographs of enteritis due to Salmonella infection in a Gila monster (Heloderma s. suspectum)]. J Zoo Animal Medicine 1987. 18 (4): 168-170
Durham, Floyd E. 1951. Observations on a captive Gila Monster. Amer. Midland Nat., vol. 45, pp. 460-470, 1 table.
Edwards, H. T., and D. B. Dill. 1935. Properties of reptilian blood. II. The gila monster (Heloderma suspectum Cope). J. Cell Comp. Physiol. 6(1):21-35, 5 fig., 5 tab.
Funk, Richard S. 1966. Notes about Heloderma suspectum along the western extremity of its range. Herpetologica 22(4):254-258.
Grasse, Pierre-P. 1970. Les glandes venimeuses et le venin des sauriens helodermatides, p. 676-680, fig. 454, In, Pierre-P. Grasse, Traite de zoologie, anatomie, systematique, biologie, vol. 14. Reptiles, Fasc 2, Caracteres generaux et anatomie. Masson et Cie Ed., Paris.
Haddon, E.P. 1954. Little monster. Outdoor Life, vol. 114, pp. 46-49, 15 illus.
Hensley, M. Max 1949. Mammal diet of Heloderma. Herpetologica, vol. 5, p.152
Kauffeld, Carl F. 1943. Field notes on some Arizona reptiles and amphibians. Amer. Midland Nat., vol. 29, pp.342-359, 4 illus.
King, F. Willis 1932. Herpetological records and notes from the vicinity of Tucson, Arizona, July/August 1930. Copeia, pp.175-177.
Komori, K; Nikai, T; Sugihara, H. Purification and characterization of a lethal toxin from the venom of Heloderma horridum horridum. 1988. Biochem. and Biophysical Research Communications. Vol 154 (2): 613-619
Koster, William J. 1951. The distribution of the Gila monster in New Mexico. Herpetologica, vol. 7, pp.97-101, map.
Mebs, Dietrich. 1968. Some studies on the biochemistry of the venom gland of Heloderma horridum. Toxicon 5(3):225-226, 1 fig.
Mebs, Dietrich. 1969. Isolation and properties of kallikrein from the venom of the gila monster (Heloderma suspectum). Hoppe-Seyler’s Z. Physiol. Chem. 350:821-826, 3 fig., 2 tab. (Germ., Engl. summ.).
Mebs, Dietrich. 1969. Purification and properties of a kinin liberating enzyme from the venom of Heloderma suspectum. Naunyn-Schmiedebergs Arch. Pharmakol. Exp. Pathol. 264(3):280. (Germ.).
Mebs, Dietrich. 1970. Biochemistry of Heloderma venom. Toxicon 8(2):142-143 (abstr.).
Mebs, Dietrich. 1970. Biochemistry of kinin-releasing enzymes in the venom of the viper Bitis gabonica and of the lizard Heloderma suspectum, pp. 107-116, 6 fig., 2 tab., In, F. Sicuteri, M. Rocha e Silva and Nathan Back (Eds.), Bradykinin and related kinins: cardiovascular, biochemical and neural actions. Plenum Press, New York.
Mebs, Dietrich. 1970. Untersuchungen ueber die wirksamkeit einiger schlangengift-seren gegenueber Heloderma-gift. Salamandra 6(3-4):135-136 (Engl. summ.).
Mebs, Dietrich, and H. W. Raudonat. 1967. Biochemie des giftes der krustenechsen Heloderma suspectum und Heloderma horridum. Naturwissenschaften 54(18):494.
Mebs, Dietrich, and H. W. Raudonat. 1968. Biochemical investigations on Heloderma venom. Mem. Inst. Butantan 33(3):907-911, 4 fig.
Michl, H. 1972. (Review of) Untersuchungen ueber die wirksamkeit einiger schlangengift-seren gegenueber Heloderma-gift, by Dietrich Mebs, 1970. Toxicon 10(2):189.
Patterson, Robert A., and In Soon Lee. 1969. Effects of Heloderma suspectum venom on blood coagulation. Toxicon 7(4):321-324, 4 tab.
Pregill, G.K.;Gauthier, J.A.;Greene, H.W. 1986 The Evolution of Helodermatid Squamates with Description of a New Taxon and an Overview of Varanoidea (Trans. San Diego Soc. Nat. Hist 21 (11): 167-292
Shaw, Charles E. 1968. Reproduction of the gila monster (Heloderma suspectum) at the San Diego Zoo. Zool. Garten 35(1-2):1-6, 3 fig.
Shufeldt, R. W. 1890. Contributions to the study of Heloderma suspectum. Proc. Zool. Soc. London 1890:148-244, 3 pl.
Stahnke, Herbert L. 1950. the food of the Gila monster. Herpetologica, vol.6, pp.103-106.
Strel’nikov, L.D. 1944. Snachenie solnechnoi radiatsii v ekologii vysokgornyh reptilii. [Importance of solar radiation in the ecology of high mountain reptiles.] Zool Zhur., Moscow, vol. 23, pp. 250-257.
Taub, Aaron M. 1963. On the longevity and fecundity of Heloderma horridum horridum. Herpetologica 19:149.
Trutnau, Ludwig. 1968. Gefangenschafts-beobachtungen an krustenechsen (Heloderma suspectum Cope). Aquarien Terrarien Z. 21(4):120-125, 10 fig.
Trutnau, Ludwig. 1970. Ein beitrag zur behandlung erkrankter krustenechsen (Heloderma horridum und Heloderma suspectum). Aquarien Terrarien Z. 23(8):251-253, photos.
Trutnau, Ludwig. 1970. Die skorpion-krustenechse Heloderma horridum (Wiegmann). Aquarien Terrarien Z. 17(7):228-231, 5 fig.
Tu, Anthony T., and David S. Murdock. 1967. Protein nature and some enzymatic properties of the lizard Heloderma suspectum suspectum (Gila monster) venom. Comp. Biochem. Physiol. 22(2):389-396, 6 fig., 1 tab.
Tu, Anthony T., and David S. Murdock. 1967. Protein nature of Gila monster (Heloderma suspectum suspectum) venom. Int. Congr. Biochem. 7th., Tokyo (abstr.).
Van Denburgh, John. 1922. Helodermatidae in Reptiles of Western North America… Vol. 1: 470-476, plt 44-47. SF Acad. Sciences
Vandermeeers, Andre; et al. Chemical, immunological and biological properties of peptides like vasoactive-intestional-peptide and peptide-histidine-isoleucinamide extracted from the venom of two lizards (Heloderma horridum and Heloderma suspectum) Eur. J. Biochem. 164, 321-327 (1987).
Vorhies, Charles T. 1917. Heloderma suspectum, automobile tourists and animal distribution. Science, vol. 68, pp. 182-183
Wagner, Ernie; Smith, R.;Slavens, F. 1976. Breeding the Gila monster in captivity. International Zoo Yearbook, Vol. 16
We are 132 days past oviposition and the remaining six eggs appear to be hanging in there. One of the eggs has dented in, which I am hoping means that it will hatch in the next few weeks and does not mean the embryo has died. The other eggs remain rigid and appear to be well, fingers crossed they come to term! The Grumbach has been great in maintaining the temperature and humidity stable throughout incubation, but I have noticed that the egg boxes have increased in temperature by 1°F higher than the incubator over the last few weeks. Condensation has also started to build up (mostly on the sides) so I’ve been keeping an eye on that to ensure none falls on the eggs potentially suffocating the embryo inside. Since the eggs were incubated at the lower end of the range it can be expected that the eggs will hatch (if they do) toward the later end of the spectrum, potentially 150+ days. Man, I can’t wait…
On the other side of the house my adult Gilas are getting ready for next year. Weekly feedings of 2-3 mice (2 for the males, 3 for the females) has brought all of the Gilas to a healthy state; good fat reserves in the tails and a constant, though not concerning, weight gain. As most of my group was purchased earlier in 2019 and after the hibernation cycle, I do not have data on what the pre-hibernation weights were last year but I think they are ahead as their weights are above pre-breeding numbers from this season. I hope to have more fertile eggs that make it to term in the upcoming season as they entire group will have been with me for the whole cycle.
Winter cooling is going to start in late November and this year a larger refrigerator / cooler is going to be purchased in order to facilitate all adults. I’ve noticed an increase in activity and feeding response in the adults over the past week, almost being as active as breeding season. I do not know if this has to do with growing follicles and testes, a reduced photoperiod, or slight drop in temperature (or maybe all) but it does seem that the Gilas are getting ready for a long winter’s nap!
That’s all for now, hopefully the next post is of the Gilas hatching!!
Not much has happened since the last update; one good egg died leaving me eight healthy growing eggs in the Grumbach incubator. A universal agreement on Gila monster eggs is to leave them the F* alone during the long incubation time. I have a hard time doing this but have been a good bean and done so by only check through the incubator’s clear door and light to make sure none are dying. The Grumbach is holding temps and humidity as it should; Temperature ranges from 77.5˚F to 79.5˚F and humidity in the incubator stays at a steady ±90% RH (relative humidity) with the Squamata Concepts S.I.M. egg boxes at 100% RH. I have three SensorPush sensors (one in each egg box, one in the incubator) connected to a SensorPush Gateway to monitor temperature and humidity. And the Gilas? All are eating and back to normal, with the females gaining weight nicely. I still find it interesting how the feeding habits changed so much during the breeding season and look forward to more data next year from this interring period of time.
I wanted to post a few photos of good eggs and bad / dead eggs (see above) and discuss a few observations. When an egg goes bad, there is no mistaking it; they begin to sweat, discolor, and smell awfully. The good eggs remain turgid and whitish in color, with increasing veining (last I checked a few weeks ago) when candled. I do not plan to open the incubator door again unless something is going wrong or an egg dies, so hopefully they are growing and not just looking good….
My next post will be one on the tools being used in my program for Gila monster breeding and incubation.
It’s been all quite on the update front as, well, there has not been much to report. Until now, that is! On Friday June 7, Gila 03 dropped one egg over the night and I came upon it at 6am when getting up for work. I candled the egg but did not see a blood ring (something that viable eggs have) but put the egg into an egg box just in case. For those that have not heard of this stuff yet, candling is using a flashlight to light up the egg to see what is going on inside. The blood ring is the blastoderm that will one day become a baby. No blood ring, no baby. Gila 03 did not drop her eggs in succession and the next one came Friday night around 10pm. This egg also did not look viable, but was more solid than the first. The third egg from 03 came Saturday afternoon and had a clear, but small (dime-sized) blood ring. I think 03 has more eggs in her, but she hasn’t dropped yet. Now when will little 05 drop her eggs….
That answer came Sunday morning when I got up around 7am and two eggs were in the nest box. Two, beautiful healthy eggs! Now, 05 is on the smaller side (757 grams pre-breeding season) so I did not expect many eggs from her but over the course of the next eight hours she would go on to lay a total of six viable eggs! Poor girl, she looks exhausted.
Now is the hardest part, incubation. I hope everything is set up right in the Grumbach S84 as I’ve had the humidity (90%RH) and temperature (79°F) dialed in for a month now. I opted to go for a lower temperature as outside temps have hit over 100°F in May so I expect the Summer to be pretty hot and I do not want the eggs exposed to high temperatures.
I’ll post some more thoughts and data that have been collected in the meanwhile, but fingers crossed the eggs make it to term and we have baby monsters in the Fall!
Gila monster 06, formerly known as Joy, was thought to be a female and was the one that was sick. Now that Joy is better, I wanted to finally determine confirm her sex (though based on head size I guessed female). My intention was not to breed, only to watch the reaction and once I put Joy in the cage with a known male (one from the group she came from) Joy went right into battle mode and started wrestling with the other male. There went that theory. The girl formerly known as Joy is now a boy named Floyd. No more gender dysphoria. You be you, Floyd.
My first encounter with this behavior was many years ago when my best friend saw the Gila monster in its cage upside down and unmoving. He called in a panic and said that my pink lizard (his reference of Gila monsters to this day) was dead. Of course when the cage was opened the lizard sprang to life and was quite aggressive upon examination. Now that I have a group of Gilas, I see this behavior often. Above are a few examples of what this looks like.
I wonder why Gila monsters do this. Is it to thermoregulate different parts of the body? Does it aid in digestion? Maybe its like having restless leg syndrome and they just can’t get comfortable! This behavior is bizarre, but I must say that Gila monsters are quite interesting and they do some funny things I have not seen other reptiles do. I think a book on captive behavior alone would be a fun read!
After keeping Gila monsters for over twenty years and having a lifelong fascination with these amazing reptiles, my first earnest attempt at breeding them has been quite fun. Don’t know how successful at this point, but it’s the journey and not the destination in my case (though seeing baby monsters pip out of the egg would be a dream come true for me).
When studying up on breeding all these years there were so many questions I had. Can you tell a male from female by head shape or appearance? Why do you need a group or colony to breed? What does male combat look like versus male to female interactions? Is it better to keep them singly or in a group when attempting to breed? So far, I have learned a better understanding of these questions and will make an attempt at answering them to the best of my knowledge at this point.
To establish a base point, and long before this breeding season, I have collected as many books on Heloderma as I could (not to mention art, toys, and other chachkies). In relation to breeding, a few books have been the guiding light to my program. First and foremost is Dr. Mark Seward’s Gila Monster Propagation. Despite being one hell of a nice guy that has answered my random emails and questions for over 20 years, his book remains to be the most thorough and introspective writing on the subject. The focus on applying the natural process of wild Gilas to captive breeding is the obvious key to success, and the one I am closely following now. Amazingly, a PDF version of the book is free on Mark Seward’s website here. Of course I’m a dork and have the first and second edition in print:) The other book I am using is a European text, called Beaded Lizards & Gila Monsters Captive Care & Husbandry by Bernd Eidenmüller and Manfred Reisinger. This is another great book that offers insight and some different perspectives into breeding and maintaining Heloderma. I’ve never heard of a Grumbach incubator before reading this book, and liked what I read about the stability of the incubator so I picked up a used one off eBay (Compact S84), tested, modified, and tested again to get the temperature and humidity right. Fingers crossed I get viable eggs to go in this wonderful machine! The other book I am utilizing right now is the venerable Biology of Gila Monsters and Beaded Lizards by Daniel Beck. There is not a specific focus on captive breeding but it does provide invaluable reference to the natural biology and behavior of Gila monsters that can be applied to breeding and has given me a lot of thought on what has occurred so far.
After acquiring the group of adult Gilas, and having the two existing adult Gilas properly cooled to a chilly 53F in a modified wine cooler from Thanksgiving to March 1st, I was good to go. Unfortunately one of my females had some blood in her stool and was ultimately brought to a vet and has been receiving medicine (this experience will be another post soon), she is out of breeding for the year to ensure she is healthy. Always, the well-being of the animal must be first priority! I jumped the gun and started putting my Gila together about the middle of March (April 1st is the recommendation from M. Seward, or 4-6 weeks out of hibernation) to see who was who. I had a good guess on how the sexing game would play out as the head shape on the animals I have were apparent side by side. Two were questionable, but my guesses were accurate. I started by rotating the new Gilas with my 21-year-old, known sexed by ultrasound male and recording the interactions. I started with the Gila that was voted most likely to be a girl with my male. Then paired the most likely male to my male, again recording the interaction. One of those interactions was posted here, and I will put up a female to male video up soon.
Boys will be boys….
The interactions between the sexes is stark to say the least. Males, when faced with another male, reacted almost immediately and the ritualized male combat started. I can see where, when faced with no path of escape, the fighting can escalate to a vicious brawl and continue to the exclusion of breeding. It is intense! After safely removing the “losing” male, or the one that leaves the cage, the remaining male roams around huffing and puffing ensuring the competition has left. Interestingly, both males, the winner and the loser in their respective cages, start raising the tails and marking their territory with their cloaca. At one point, the winner had his hemipenis everted and he rubbed it about his cage. I then introduced a female into the cage. The interaction between males and females in my group could best be described as gentle, even romantic (in lizard terms) as both sexes start licking the air madly, picking up on the scent of the opposite sex. They then approached each other and continued tasting the air and each other with their tongues. It is a much slower pace than the instant male to male interaction, and eventually the male starts to chase the female around the cage in an attempt to copulate.
No Means No!
Even in the animal kingdom, no means no. In my case, the females that have been introduced into male cages have been, to my observations, not ready or unwilling to copulate. Did I introduce them to early? Have I somehow missed the short window that the female produces mature follicles? Time will tell at this point as I have not witnessed copulation in my group. The females, when, um, mounted by the males either run away and hiss or bite the male and then run away. But, after the initial night’s excitement the Gilas seem to pair up and are close to each other when resting or lounging around the terrarium. The Gilas are more active at night, and perhaps this is when copulation is taking place but as of right now I cannot know for sure. I did break out my old night vision monocular the other night to observe the pairs but saw more of the same; the females running from the males when approached. I kept the pairs together for a week and have rotated the females to different male’s cages in hopes there will be some compatibility between the pairs.
Q & A
So, I asked a few questions above that I will attempt to provide answers for based on my interpretation of what has happened with my Gilas. Please keep in mind that this is still new to me and I am answering on observations made in my group of Gilas. If different revelations or findings occur, these answers will be updated.
Q – Can you tell a male from female by head shape or appearance?
A – Yes and no. When I had only two Gilas and no idea of their sex there was no known commodity for each and no basis for comparison. If you buy or own a single Gila and do not have a friend with a colony or some known sexed animals I do not think an accurate determination could be made. When I bought the colony, it still wasn’t apparent who was who, but after a few days and taking measurements I made an uneducated guess based on this factor. By sheer luck I turned out to be right but still had to put them together to be 100% sure. Check the photo above and see if you can tell the difference. Not too easy, huh? I plan on doing other comparisons of the sexes on a future post.
Q – Why do you need a group or colony to breed?
A – While I cannot definitively answer this, it appears that the social structure of Gila monsters lends itself well to groups than single pairs. I am sure offspring can be had from just one pair, but I do not know how successful breeding would be overall. I do not think if I had just one pair at this point my chances would be that good. All successful Gila breeders I have spoken with recommend group breeding.
Q- What does male combat look like versus male to female interactions?
A – Male combat is a contest where the fighters engage each other head on, and aggressively. Male to female is overall a more gentle approach. Check out my YouTube channel to see the different interactions between my lizards.
Q – Is it better to keep them singly or in a group when attempting to breed?
A – From a maintenance standpoint, I believe keeping Gilas separately is the best way to go. If the one Gila that is sick was contagious, she may have spread it to the colony and my breeding hopes would have been dashed for the year and some of the Gilas may have died. Not to mention the vet bills increasing exponentially! Also, if a lizard has an issue or isn’t eating it is easier to tell when housed singly. For my breeding program I like to see how each Heloderma suspectum reacts to one another.
I will keep updating this blog as time goes, and feel free to email me with any questions or comments especially if you have successfully bred Gila monsters and can give some guidance.
Breeding season is upon me, and it couldn’t be more exciting! As this is my first time working with a group of Gila monsters, I was unsure of what male-to-male combat looked like versus male-to-female interactions. In books they look similar but from what I have seen so far it is a very different interaction. Now, I must say that my intention was not to stimulate breeding but to confirm the sexes of the lizards in my colony. I have read that male combat can be vicious in captivity as there is no escape for the subordinate male and can certainly see how it can escalate to this level after seeing my males briefly duke it out. I find it interesting that males do not waste time getting into combat when introduced to one another, while males and females take some time to find each other and the ensuing interaction is much more gentle (though, I have seen the females bite the males on several occasions so far). This is the first step in breeding, and has been very interesting to see these reptiles interact.
Below are a few videos shot on my Leica X Vario to help others see what male combat looks like in captivity. Please note that I was around the whole time during this interaction to ensure things did not get out of control. There was some biting in the beginning but it turned into a wresting match.
I recently picked up a small breeding group (3.3, or 3 males and 3 females) of adult reticulated Gila monsters so my dream of breeding these amazing reptiles is within reach. Today, with the help of a friend, we measured, weighed, photographed, and documented all of the new Gilas pre-breeding season. They have been in hibernation since November and were pulled a few weeks early so I hope what needed to be done biologically is done.
My original two males are still in hibernation until the first of March. I will be updating this blog throughout the breeding season to document my successes, and failures. I have my Grumbach incubator dialed in and ready so all I need are some eggs!