It turns out to be much more intense than with encounters between males. The investigators even had to intervene to prevent the brawl from getting out of hand.
You may think that males generally fight rougher than females. But that is certainly not the case among gila monsters. Female gila monsters prove surprisingly vicious. Investigators were truly amazed at the perceived aggression.
Let’s get ready to rumble!
In the study, researchers got several adult gila monsters to fight each other. The intention was to collect data on their bite force. The team also wanted to study to what extent the osteoderm (a hard, bony inclusion in the skin in the form of a scale) provides sufficient protection during violent encounters.
More about gila monsters
Gila Monsters (Heloderma suspectum) are large, venomous lizards, mainly found in the dry and arid deserts of the United States. They are easy to recognize animals: the body is black with red to pink spots and they have a warty scaly skin, caused by osteoderms. In addition, they are equipped with huge teeth. The fat tail serves as fat storage for times when less food is available. In this way they can go without food for a month. Gila monsters can grow over two feet in length. And at this impressive length, it is the largest native lizard in the United States. In general, gila monsters live to be about 30 years old. The animal is named after the area of the Gila River in Arizona, where they were once abundant.
In all four trials, the female gila monsters came to blows right away. And the fight escalated remarkably quickly. In fact, the encounters turned out to be much more intense and violent than those between males.
Males vs females
“Males actually wrestle,” explains researcher Kristopher Lappin. “They can bite at each other, but as far as we know, they don’t bite each other so hard that it really hurts. Based on our experiments, we now know that females do bite each other intentionally. In three of the four encounters, we had to intervene to prevent them from seriously injuring each other.”
Before the females attacked each other, they first made warning tongue movements. Then came hissing noises, followed by shoving and scratching, as they reared themselves. And then the fight started. The females grabbed each other with their large teeth and then did not let go. In this state they spun around, similar to the so-called ‘death roll’ of crocodiles. Whenever they rotated in this way, the experiment was stopped and the researchers separated the females to avoid serious injury. None of the gila monsters were permanently injured.
While the researchers had expected the females to be aggressive, they were surprised by how quickly the situation escalated. They did not expect the fighting to be so intense and violent. In addition, the gila monsters that had been bitten – and thus had poison in their bodies – were pretty bad for a few days. It took them some time to get back on their feet, both physically and mentally. Fortunately, they succeeded on their own; no medical intervention was needed to cure the animals.
The question, of course, is why females are so extraordinarily aggressive. We know from studies of other lizard species that females show aggression when defending their territory or mate. Even when they have become mothers and protect their young, they sometimes want to lash out. While this could also be the reason for gila monsters, the researchers also have another suspicion. The gila monster’s menu mainly consists of eggs from birds or reptiles and they also sometimes empty mammal nests. The observed female aggression may be an effective way of scaring away conspecifics to prevent cannibalism.
Enough to learn
Whether this is indeed the case will have to be determined in future research. Moreover, there is still enough to learn about these fascinating animals. “Despite their iconic status as large, venomous lizards, Gila monsters have been largely under-researched,” notes study leader Gordon Schuett. “Interestingly, certain components of their venom have been used in the development of drugs for type 2 diabetes since the early 2000s. The study provides new knowledge about the social structure of this endangered species.”
Indeed, because apparently female gila monsters are not very friendly to each other. “Aggression between female gila monsters is a good example of what aggressive behavior can look like and how extreme it sometimes is,” Lappin concluded. “It plays an important role in social structure and reproduction. We hope that this study will lead to more research into this behavior, both in this iconic species and in other animals.”