A Northern Pacific rattlesnake. Image taken at the California Academy of Sciences.
Rattlesnakes! Very common and very venomous snakes on the west coast and fascinating reptiles to learn about. Where to begin? I suppose the most common questions I’ve encountered about snakes have to do with their venom and the way they catch and kill food.
Humans are most likely to have problems with rattlesnakes when the snakes are feeling threatened and are defending themselves. Venom is actually very energy expensive to make and not beneficial to the snake to waste, so if a snake is aware of you and it can get away, it is likely to disappear before you’ve even noticed it. But, if you do cross a rattlesnake and it is threatened, usually it will give you a warning by shaking its rattle as a threat. Usually. Young rattlesnakes do not yet have a rattle, and the pieces or “beads” of its rattle will come with each shed. (You can’t actually tell how old a rattlesnake is by its rattle because pieces of the rattle can fall off and the number of sheds a snake has varies.)This fact is most unfortunate, because young rattlesnakes are actually more dangerous than adults. Adult rattlesnakes control the amount of venom they use to try to conserve it, whereas the young don’t hold back venom.
There is another reason why this warning is sometimes absent. Humans are selecting against it. Human fear of rattlesnakes often causes them to kill rattlesnakes when they are discovered. Therefore, the snakes that don’t make their presence known are the ones that are surviving and reproducing. Apparently, the number of rattlesnakes not giving this warning anymore is significantly increasing. So thank you, ignorant humans.
A Northern Pacific rattlesnake's rattle and its distinctive stripey tail. Image taken at the California Academy of Sciences.
In any case, usually a rattlesnake will rattle and hopefully the creature that stumbled too close respects the warning. If not, the rattlesnake will bite to defend itself. Sometimes the bites are “dry bites,” where the snake bites but does not inject venom. And sometimes they are not. The NIH has some excellent suggestions for how to avoid snake bites and what to do if you are unfortunate enough to get bitten here. My favorite piece of info gleaned from this site? Don’t pick up dead snakes because they can still bite up to an hour after death. ZOMBIE SNAKES!!! (Or a really strong biting reflex.)
So, venom and rattle are a great defense. So great that rattlesnakes even have non-venomous mimics. Gopher snakes have a similar coloration to some types of rattlesnakes and will shake their tail in dry leaves and hiss to mimic the sound and the appearance of a rattle. Rattlesnake defense is very important because far from being top predators, these animals are right in the middle of the food chain. Various birds of prey, especially red-tailed hawks are known to consume these snakes.
Venom does not always work as the best defense, however. Kingsnakes, for example, are immune to rattlesnake venom and will eat rattlesnakes. Ground squirrels are also immune to Northern Pacific rattlesnake venom and will exhibit mobbing behavior, aka ganging up on them. So these animals have a lot to worry about.
But, they are not always the victim. They are also the hunter. Awesome hunters. Rattlesnakes have an extra sense to help them hunt. Take a look at the image below. See the big circular spot under his eye, above his mouth?
A Northern Pacific rattlesnake. Note the circular heat sensing pit. Image taken at the California Academy of Sciences.
This is a heat sensing pit. So, when you hold your hand over a stove, you can tell its hot without touching it right? Well imagine if that sense was so strong, you could feel the body heat of a furry creature at a distance. That’s what that pit does. So, even if the wind is blowing in the opposite direction and the snake can’t smell food, it can still find its prey. Neat, huh? And it uses its venom to hunt as well. This rattlesnake pictured here will bite its prey and let it go, but follow it until the animal stops running. The venom will actually partially digest the animal for the snake before it gets to it.
They’re not just great predators and great defenders, but the Northern Pacific rattlesnake is also one of the few snakes to exhibit any form of “parental care.” That is, young rattlesnakes are allowed to stay with their mother for a few weeks and gain protection from her presence. When its time to hibernate, they follow their mother’s scent trail to the same den year after year. Some of these dens have been occupied for over 100 years!
And one last way that these snakes might surprise you…they are actually great swimmers and have even been found several miles out to sea.