Tag Archives: rattlesnake

Rattlesnakes modulate their tail wagging to make you think they’re closer than they are

The rattling of rattlesnakes isn’t as simple a warning as we assumed. New research explains that this sound is subtly modulated to change the listener’s perception of its source, making it seem the snake is closer than it actually is.

Image via Pixabay.

Rattlesnakes are quite famous for the warning sounds they produce with their tails, the iconic ‘rattling’ that gives them their name. Far from being a simple wagging of the tail, however, new research suggests that this rattling is a fine-tuned intimidation tool. As the snake rattles its tail, it makes an abrupt shift to a high-frequency mode, the team explains. This makes listeners perceive the source of sound as being closer than it actually is.

In effect, while definitely being deadly, rattlesnakes also engage in some strategic deception.

Rattle my bones

“Our data show that the acoustic display of rattlesnakes, which has been interpreted for decades as a simple acoustic warning signal about the presence of the snake, is in fact a far more intricate interspecies communication signal,” says senior author Boris Chagnaud at Karl-Franzens-University Graz. “The sudden switch to the high-frequency mode acts as a smart signal fooling the listener about its actual distance to the sound source. The misinterpretation of distance by the listener thereby creates a distance safety margin.”

Past studies have shown that rattlesnakes’ rattles vary in frequency, but they didn’t give us any insight into why they do, or what this behavior actually achieves in the real world.

The hypothesis behind this paper was born while Chagnaud was visiting an animal facility and noticed that rattlesnakes increased the frequency of their rattling as someone approached the snakes — but decreased when they walked away. From this observation, Chagnaud and his team developed an experiment in which objects appeared to move towards rattlesnakes. One of these objects was a human-like torso, and another was a looming black disk. The illusion of forward-back movement was created by making the objects increase or decrease in size.

The team reports that over the course of this experiment, as potential threats approached the snakes, they would increase the frequency they rattled at to approximately 40 Hz. But, abruptly, they would switch to an even higher frequency range, between 60 and 100 Hz.

Further experimentation revealed that rattlesnakes adapt their rattling frequency to the (perceived) approach velocity of an object, rather than its size.

“In real life, rattlesnakes make use of additional vibrational and infrared signals to detect approaching mammals, so we would expect the rattling responses to be even more robust,” Chagnaud says.

Inside a virtual reality environment, the team then tested how this shift in rattling frequency is perceived by a person or animal close to the snake. A group of 11 participants were asked to engage in a simulated walk inside the virtual environment — a grassland — and told they’ll be walking towards a snake. Its rattling rate increased as the participants closed in, as per the previous findings, and suddenly raised it to 70 Hz at a virtual distance of 4 meters.

The participants were asked to tell the team when the rattling sounded like it came from only 1 meter away. All the participants underestimated the distance that the virtual snake was at after it increased its rattling frequency.

“Snakes do not just rattle to advertise their presence, but they evolved an innovative solution: a sonic distance warning device similar to the one included in cars while driving backwards,” Chagnaud says. “Evolution is a random process, and what we might interpret from today’s perspective as elegant design is in fact the outcome of thousands of trials of snakes encountering large mammals. The snake rattling co-evolved with mammalian auditory perception by trial and error, leaving those snakes that were best able to avoid being stepped on.”

The paper “Frequency modulation of rattlesnake acoustic display affects acoustic distance perception in humans” has been published in the journal Current Biology.

Pecos River style pictographs in Rattlesnake Canyon. You can see a rattlesnake depiction on the left of a dark shaman figure. Credit: Steve Black.

Fossilized poop shows ancient hunter-gatherer ate a rattlesnake whole — fangs included

A rattlesnake fang found in 1,500-year-old fossilized poop. Credit: E. M. Sonderman.

A rattlesnake fang found in 1,500-year-old fossilized poop. Credit: E. M. Sonderman.

More than 1,500 years ago, a really brave hunter-gatherer ate an entire rattlesnake, including its one-centimeter-long fangs. We know about this because the fangs and other traces of the snake were pooped out, becoming fossilized as coprolites which archaeologists discovered in a rock shelter in southwest Texas. This is the first evidence of whole-snake consumption in the fossil record.

These coprolites were part of a collection of over 1,000 such samples collected during the 1960s in Conejo Shelter, found in Lower Pecos Canyonlands, Texas. Archaeologists believe that humans have inhabited the region for 12,000-14,000 years. Judging from the quality and quantity of coprolites found at the rock shelter, the site seems to have served the role of a latrine.

Analyzing ancient poop under a microscope might not sound like the glamorous work you’d expect to see in movies about archaeology. But, in reality, this kind of work can be quite exciting. By studying fossilized feces it is possible to discern what ancient people’s diets looked like thousands of years ago, essentially learning more about their way of life than most ruins or shards of pottery could ever reveal. The individual also consumed an assortment of plants like Agave lechuguilla and Liliaceae flowers, Dasylirion fibers, and an Opuntia cactus.

Pecos River style pictographs in Rattlesnake Canyon. You can see a rattlesnake depiction on the left of a dark shaman figure. Credit: Steve Black.

Pecos River style pictographs in Rattlesnake Canyon. You can see a rattlesnake depiction on the left of a dark shaman figure. Credit: Steve Black.

The coprolites were carbon dated to around 1,500 years ago, almost a millennium before the first European set foot on the continent. These pre-Columbian hunter-gatherers who lived in the region likely had to deal with quite a lot of adversity during that time. The harsh desert conditions mean that there wasn’t that much food to forage, so anything that an individual could find to eat was precious, whether rodents, rabbits, or even venomous snakes.

However, this eccentric hunter-gatherer likely didn’t consume the rattlesnake for substance. Instead, researchers have a hunch that the viper — which was either a western diamondback rattlesnake or copperhead — was devoured whole for ritualistic purposes. It’s not uncommon for people of that age to consume venomous snakes, but they would do so only after removing the heat, rattle, and skin prior to cooking. Secondly, the other foodstuff found in the same coprolites samples suggests that the hunter-gatherer wasn’t particularly starving or desperate for food. Another clue that the snake dinner might have been part of a ritual lies in the rock art made by Lower Pecos people, which frequently depicts snakes.

“Future analyses of coprolites from this lens and the surrounding contexts will further our current understanding of this unique gastrological event and better situate it in the context of diet patterns and paleoenvironmental adaptions in the Lower Pecos,” the authors wrote.

The findings appeared in the Journal of Archaeological Science: Reports.



Contrary to popular belief, drought actually leads to fewer snakebites

There are many myths and popular beliefs regarding snakes — but this one certainly isn’t true.

Image credits: Noah Loverbear.

A few years ago, Grant Lipman, an emergency medicine physician at Stanford Medicine, was jogging on the hills around campus. It was a terrible drought, but that wasn’t the highlight of his day — the highlight would be a 3-foot-long rattlesnake lying on the trail. He discussed this with his colleagues, and one of them reported a similar sighting. This got Lipman thinking. Could the drought be in any way connected to the rattlesnakes they were seeing or was it simple coincidence?

“I wondered if there are more snakebites during droughts,” said Lipman, clinical associate professor of emergency medicine at the Stanford School of Medicine, who routinely treats patients with venomous snakebites.

So he started work and worked with a team of researchers to answer the question.

Everyone sure seemed to believe that droughts exacerbate snakebites. “Deadly Snakebites Set to Skyrocket During Record-breaking Drought,” read one article in 2018 in the Daily Mail. Another, “Snakes Cross Paths with Humans in Bay Area Due to Drought,” was reported on ABCNews.com in 2015.

It seemed to make some sense. The idea was that snakes are more active during warm weather, and they also need to wander more during droughts. But the scientific information was pretty scant on the subject.

The results, funnily enough, showed that the opposite is true: during dry spells, snakebites actually go down.

Lipman and colleagues analyzed 20 years of snakebite data from every phone call made to the California Poison Control System from 1997 to 2017. In total, 5,365 snakebites were reported, from rattlesnakes. Five of them were fatal. The number of bites varied significantly from county to county, ranging from 4 to 96 per one million people.

It was actually rain that seemed to get the snakes out.

Snakebites went down by 10% following a drought but increased by 10 percent following high levels of precipitation. Researchers believe that this happens because, during the rainy season, shrubs grow more, which also favors rat populations — snakes’ favorite prey.

The study isn’t frivolous — this isn’t only about satisfying a curiosity. It can be quite important, and potentially even save lives. By knowing when snakebites are more and less likely to happen, authorities and hospitals can stockpile and transfer antivenom — which is often a scarce commodity, accordingly.

But Lipman, who has vast experience on treating this type of bite, says that the best way to reduce the frequency of bites is to simply be more careful. Snakes never go out of their way to attack anyone, quite the opposite — they go out of their way to avoid people as much as they can.

“The most common comment I usually hear from snakebite victims in the emergency room is: ‘I was just minding my own business,'” Lipman said. “Usually, though, it’s the snakes that were minding their own business, having a nice nap. It’s people who tend to disturb them.”

Fungal disease ravages American rattlesnakes

Scientists still haven’t found a cure or a solution for the disease, with cases being confirmed in at least fifteen US states and several countries in Europe.

Northern water snake (Nerodia sipedon) with crusty and thickened scales overlaying raised blisters as a result of a fungal skin infection, captured from an island in western Lake Erie, Ohio, in August 2009 (case 22747). Photograph by D.E. Green, USGS National Wildlife Health Center.

According to National Geographic, fungal diseases have run rampant in the past few decades, attacking populations of frogs, bats, and salamanders. Snakes are the latest to fall victim to such a disease. Although it’s hard to gauge its damage due to the cryptic nature of snakes, researchers fear consequences can be devastating, especially if action is delayed.

Snake fungal disease is caused by a pathogen called Ophidiomyces ophiodiicola, with the most common symptoms including skin swelling, crusts, and nodules of the skin. However, lab studies have also revealed other fungi associated with Snake Fungal Disease (SFD), so it’s hard to say that there’s only one pathogen responsible. Skin lesions often occur, which can develop into full-grown blisters that disfigure snakes, potentially leaving them unable to feed themselves.

snake fungal disease

Milk snake (Lampropeltis triangulum) showing signs of fungal and bacterial infections, captured in Westchester County, New York, February 2013 (case 24281). Photograph by D.E. Green, USGS National Wildlife Health Center.

So far, over 30 species have been found suffering from the diseases, but one group of snakes is especially vulnerable to the disease: rattlesnakes.

We don’t know why rattlesnakes are more threatened by the fungal diseases, just as we don’t know why these diseases sometimes pop up more than other times. Jonathan Kolby, an American biologist and conservationist, comments:

“It just seems one after the other that these emerging fungal diseases are appearing in different types of animals, yet they’re spread enigmatically,” said Kolby, who is also a National Geographic explorer. “We don’t know where exactly they came from or why they suddenly appear to be more virulent.”

As it’s often the case with such infections, it’s not necessarily a case of the pathogen growing stronger, but rather a case of the host growing weaker. If this is at work here, then it could mean that snakes are under environmental stresses which don’t allow them to defend properly. Moving on with that line of thought, if we want to find the cause of this disease, we have to look at what changed in their habitat. A likely culprit is climate. Jeffrey Lorch, a microbiologist at the United States Geological Survey, explains:

“It could be that if we’re experiencing cooler and wetter springs in which snakes have to spend more time underground and not be able to reach those high body temperatures necessary to fight off infection that it could leave them more susceptible,” he said.

Habitat destruction is also eating away at the snakes’ lifestyle. The problem, again, is that we still have many gaps in our understanding of snakes, because they’re notoriously difficult to study — they spend most of the day hidden and hide underground when it gets too cold. To make things even worse, snakes aren’t particularly popular, to say the least. As a result, the snake fungal disease research community is quite small, and data is scarce and unreliable.

Jennifer Moore and her research team at the Pierce Cedar Creek Institute in Hastings, Michigan, are some of the few scientists working on the issue. She is trying to develop a long-term dataset focused on the eastern massasauga rattlesnakes. The University of Illinois is also working on treatments for infected snakes. At this moment, the problem seems to be concentrated in the US, but cases of SFD have also been reported in snakes in captivity in England, Germany, and Australia, Kolby said.

“I’m concerned about spillover and introduction to other countries if the United States might be the point source,” he said. “I think that deserves more attention from other countries, too.”

Snakes play an important role in ecosystems, basically serving as nature’s pest control. Most snakes are middle-order predators, which means that they eat other creatures, but they too can be eaten by higher-order predators. Having these creatures which can be both predators and prey gives ecosystems stability and resilience.