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.

Thanks for stopping by Goatsby’s Place!

Adam