heat sensor


There are 17 species or subspecies of rattlesnakes in Arizona and they all object to being stepped on. So watch where you walk. In my field experience as a geologist, I’ve encountered many rattlesnakes (26 on one morning), and most of the time they don’t rattle. They prefer to remain inconspicuous. See here for a list of all recognized rattlesnake species and subspecies.


Some herpetologists regard rattlesnakes as one of the most highly specialized animals on the planet. The venom, a toxic saliva, is a complex mixture of enzymes that include hemotoxins, that attack the blood and start the digestion process in tissue, and anticoagulants. The Mohave rattlesnake also carries neurotoxic venom that may cause circulatory arrest or respiratory paralysis. That said, however, fewer than 1% of people bitten in the U.S. die as a result of the bite, but many sustain tissue damage. About 20% of defensive bites are dry – no venom injected. Venom is injected via curved fangs which fold back into the snake’s mouth. Rattlesnakes seem to have spare parts to replace damaged fangs. Baby rattlesnakes are venomous and ready to go, they just can’t inject as much venom as a larger snake.

If you are bitten, the University of Arizona College of Pharmacy recommends that you get to a hospital to get antivenom and treatment for tissue damage. Don’t bring the snake; the antivenom treats all bites. Also don’t use tourniquets, that just concentrates the venom and produces more tissue damage. Don’t use ice for the same reason. Don’t cut and suck; you can’t get enough venom out to make a difference, and, if a friend does it for you, he takes a chance of envenomating himself. Do remove tight clothing, shoes, jewelry from the affected limb.

Rattlesnakes are pit vipers, which means they have heat-sensing organs located between their eyes and nose. A rattlesnake can detect the heat of a candle at 30 feet. Some researchers claim that a rattlesnake can perceive a temperature difference of as little as 0.01 degree Fahrenheit at one foot. The snakes use this heat-sensing ability in several ways. They can follow the heat trail of prey even in total darkness. They can tell if an animal is too large to be prey and thereby avoid it. And, the exothermic (cold-blooded) snake can use their temperature sensor to help find places to properly regulate body temperature.

Rattlesnakes are most active in the warmer times of year, but in Arizona, they may be out and about any time the temperature is between 70 and 90 degrees F.

Rattlesnakes are born live, rather than hatch from eggs. The babies have the first segment of the rattle, but can’t make a noise until it sheds and gets another bead on its rattle. Mother rattlesnakes care for their young at least until after the first shed. It is a myth that you can tell the age of a snake by counting the beads on the rattle. Beads are added at each shed, and the snake may shed several times a year. The rattle material is keratin, the same as your fingernails. There isn’t anything inside the rattles; the noise comes from the segments bumping against each other as the snake vibrates its tail up to 60 times per second.

Rattlesnake eyes have slit pupils like cat eyes. The gopher snake, a non-venomous constrictor, is often mistaken for a rattlesnake, but it has round pupils and lacks the triangular head of the rattlesnake.

Other snake myths. Snakes cannot dislocate their jaws. They can open their mouths very wide because they have two jaw joints on each side separated by a (quadrate) bone. Snakes also lack bony chins. Each half of the lower jaw is separated by cartilage which enables the snake to move the lower jaws independently.

Rodents are the main prey of the rattlesnake, so the snakes provide a valuable service. They also take birds, lizards, and baby rabbits and squirrels.

At the Arizona-Sonora Desert Museum, the staff capture an average of 100 rattlesnakes per year on the grounds. After capture, the snakes are marked by color-coding the tails and, more recently, by inserting a radio chip to allow tracking. The snakes are released on the far reaches of the grounds. Rattlesnakes, however, are very territorial, so many return. So, if you are at the Museum and see a rattlesnake with a multi-colored tail, you will know that particular snake is a return visitor. And no human visitors have ever been bitten by a rattlesnake at the Museum.