https://phys.org/news/2019-01-mojave-rattlesnakes-life-threatening-venom-widespread.html

To discover which venom type occurs where, herpetologists—the amphibian-and-reptile-loving scientists—have been collecting data on Mojave rattlesnakes in the Southwest. However, it wasn't until a recent publication by Clemson College of Science postdoctoral researcher Jason Strickland and professor of biological sciences Christopher Parkinson that the extent of the distribution was better understood. Their findings show a peculiar variability in the species.

"Prior to this paper, the 'herp' community thought that hemorrhagic venom was really rare and was only in one location in Arizona and one location in Mexico, but we show that it's found in several places throughout the snake's distribution," Strickland said. "There were a few instances when individuals in our sample had both types of venom, which our data suggest are hybrids."