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Do you know how many species of poisonous snakes live in the Chihuahuan Desert and on the Llano Estacado?

One West Texas rancher speaking to his daughters said this of rattlesnakes: "Rattlesnakes are not evil. God put them here, to teach us. They teach us to respect the land. They never ever attack people just to hurt us - we are monsters to them, huge clumsy monsters. Rattlers rattle at us to tell us and cows - and buffalo back in the old days - that they want everything to go around them and not step on them. They only bite us when we are being careless, or when we are trying to kill them and do a bad job of it. We did not put the rattlesnake on this Earth, girls, and we do not have the right to rid the Earth of them."

But not all rattlesnakes are the same, nor is their venom the same. Most rattlesnakes have Hemorrhagic toxins that work fairly slowly, causing tissue destruction, then hemorrhaging if the bite is severe, but it's rarely fatal in humans. The Mojave rattlesnake is dreaded for good reason. It is the only rattlesnake in the United States with a neurotoxin, which causes rapid, respiratory constriction or paralysis, and then heart failure in mice and kangaroo rats, their favored prey, but they actually rarely kill humans.

The folktale that Mojave Rattlesnakes have recently emigrated east of the Pecos River has become a widely accepted belief. A half-dozen "positive specimens" have been brought to the Sibley Nature Center to prove science wrong - but when the dead snake gets to the Sibley staff, somehow it has turned into a Diamondback Rattlesnake. Mojave Rattlesnakes don't live anywhere on the east side of the Pecos River. Less than a hundred specimens of Mojave rattlesnakes have been scientifically collected in New Mexico, and most of those come from the far southwestern boot heel of the state. A few have also been collected in New Mexico northeast of the Guadalupe Mountains. In Texas they have been collected in Brewster, Presidio, Hudspeth, and Culberson counties.

The Llano Estacado only has three species of rattlers - the diamondback, the prairie and the desert massasauga. The breaks on the east side of the Llano have the western massasagua. West of the Pecos are the mottled rock rattlers and the blacktailed rattlesnake.

Some other poisonous snakes are also found in the region. The Trans-Pecos also has the Trans-Pecos copperhead. Coral Snakes can be found in the Edward's Plateau east of the Pecos River. Cottonmouths, water moccasins, are found in the Concho and San Saba watersheds.

Another commonly heard myth in West Texas is that humans and feral hogs kill every rattler that rattles, so the only rattlers left aren't rattling anymore. It appears there is a general consensus among academic biologists that it's unlikely that rattlesnakes have become quieter and have stopped rattling. Individual snakes have "personality" - siblings kept under the same conditions can have extremely different behavior. Most of the time, however, rattlesnakes do not rattle, unless they feel threatened. Their primary defense is not being seen. As long as they feel they're not being seen, they lie quiet and let whatever potential predator there is wander by. Only when the animal has been disturbed or it's quite clear they've been spotted will they go ahead and rattle.

Avid naturalists, working cowboys and other folks often out in pastures rarely see rattlers. Unless specifically looking for them, less than a half dozen are seen a year.

Nature Notes is sponsored by the Dixon Water Foundation and is produced by KRTS Marfa Public Radio in cooperation with the Sibley Nature Center in Midland, Texas. This episode was written by Burr Williams of the  Sibley Nature Center.