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With their formidable appearance, unique rattle, and prominent place in folklore, rattlesnakes are doubtless the most legendary snakes in the United States.

I’ve encountered lots of rattlesnakes, including sidewinders, western diamondbacks, speckled rattlesnakes, Mojave rattlesnakes, and Pacific rattlesnakes, in my travels through the desert Southwest. I’ve even caught a few, and encouraged a few more to move off the road — with varying degrees of success — so they wouldn’t get run over.

I’ve never seen a rattlesnake in New England. But they are here. In fact, in September a woman saw a 5-foot-long timber rattlesnake while she was hiking in the Blue Hills Reservation, just south of Boston.

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“Massachusetts rattlesnake populations have contracted substantially in the past 150 years,” said Mike Jones, state herpetologist for the Massachusetts Division of Fisheries and Wildlife. “Historical records indicate that they were formerly widespread in Massachusetts, north and west of Plymouth County. For example, rattlesnakes were widespread on the North Shore in Lynn, Peabody, Manchester-by-the-Sea, Essex, Ipswich, and probably several other towns in Essex County. Rattlesnakes were also widespread on bedrock hills in the Connecticut and Housatonic Valleys.”

Timber rattlesnakes, which are state-listed as endangered and protected by law, are still found in five areas of Massachusetts, Jones said, including portions of Berkshire County, the Connecticut River Valley, and the Blue Hills. These remaining populations are generally very small and isolated, with the total number of timber rattlers in the state estimated in the low hundreds.

Rattlesnakes formerly lived in all six New England states, but they are now wiped out in Maine and Rhode Island. They are endangered in the other four states, and in general, New England rattlesnakes now live in only a handful of mountainous areas, Jones explained.

“Historically, rattlesnakes were purposefully eradicated by people,” said Jones, “and that legacy defines their distribution and conservation outlook today.”

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In the western part of the country, many western species of rattlesnakes are still quite common. Rulon Clark, a biology professor at San Diego State University who has studied timber rattlesnakes, said that by contrast, timber rattlers aren’t that common across their range, especially in the Northeast, where they’ve been more heavily impacted by human development and historical destruction.

“In most parts of their range, I would characterize timber rattlesnakes as almost relictual, just hanging on in a few spots where they managed to escape human efforts to wipe them out,” said Clark. “Historically, I think timber rattlesnakes would have been a very common and abundant woodland predator, the way desert-dwelling snakes like western diamondbacks can still be dominant predators in their environment.”

Timber rattlers are found as far south as northern Florida, and west to Minnesota and Texas, according to MassWildlife’s timber rattlesnake webpage. They typically grow 3 to 5 feet long, have triangular heads and vertical pupils, and large, thick bodies that vary in color from yellow to black to banded with black or brownish colors. They give birth to five to nine young in late summer.

William Brown, a retired Skidmore College biology professor who studied timber rattlesnakes, said what people might find most surprising about them is that they can live for such a long time.

“Documented longevity in the wild is 51 years,” said Brown, “with many snakes surviving into their 30s or 40s, at least in relatively undisturbed populations removed from harassment or predation by humans.”

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The primary threats to rattlesnakes are road mortality, people unexpectedly coming upon a rattlesnake and killing it because they’re frightened by it, and the combined effects of other causes of mortality, Jones explained. For example, some rattlesnakes are affected by a fungal disease that can cause serious lesions. Rattlesnakes, especially younger ones, also are vulnerable to predators, including raptors and midsized carnivores like foxes, fishers, and coyotes.

Timber rattlesnakes are dormant during cold weather, explained Jones, and generally overwinter in underground dens in rocky areas from October to April. They sometimes share overwintering sites with racers, copperheads, garter snakes, and other snakes. During the summer, timber rattlers move into surrounding forests to forage for food.

Timber rattlesnakes feed on a variety of small mammals, including chipmunks, squirrels, voles, and mice, but they’ll feed opportunistically on other animals, including birds and amphibians, said Jones.

Clark said timber rattlers are ambush predators, and often sit and wait motionless in a striking position along the edge of animal runways, such as logs, that are frequently used by rodents.

Rattlesnakes are pit vipers. According to Roger Conant’s “Field Guide to Reptiles and Amphibians,” pit vipers have a pit located on either side of their head about midway between the eye and the nostril. The pits act as sensory organs that help the snakes detect and aim at warm-blooded prey when they strike. Rattlesnakes and other pit vipers, like copperheads and cottonmouths, kill prey by injecting venom through their hollow fangs.

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Few things get my adrenaline pumping more than the sound of a rattlesnake rattling. In my experience, most rattlesnakes are very cryptic and blend in quite well with their background, where they tend to lay motionless, trying to avoid detection. Rattlesnakes use their rattle to warn potential predators to stay away, and usually they don’t rattle until you get close to them. The rattle does sound like a rattle when the snake shakes its tail slowly, but when it really gets ticked off and cranks up the speed, the sound is more like a loud buzzing noise. While rafting the Grand Canyon a number of years ago, I remember our guides referring to rattlesnakes as “buzzworms.”

The rattle is composed of loosely interlocking segments of keratin, the same protein our fingernails are made of, according to a KQED NPR program on rattlesnakes. When these segments click against each other, they produce the characteristic rattling sound we associate with rattlesnakes. They can shake their tails 50 to 100 times per second and can rattle non-stop for up to two hours. Rattlesnakes generate a new segment on their rattle every time they shed their skin, according to Conant’s “Field Guide,” and two to four new segments are typically added to the rattle each year. The older the rattlesnake, the longer the rattle, unless part of it breaks off.

Jones said other snakes, including milk snakes, hognose snakes, water snakes, and black racers, are sometimes mistaken for rattlesnakes, due to their size and color patterns. He said some snake species, including milk snakes and racers, will vibrate their tails when frightened, which might also make people mistake these non-venomous species for rattlesnakes.

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Venomous snake bites are rare in the Northeast, and MassWildlife says timber rattlesnakes do not pose a serious threat to people when left alone. In the unlikely event of a bite by a venomous snake, the prevailing advice is to remain calm and get to a hospital as quickly as possible, said Daniel Keyler, a pharmacology professor at the University of Minnesota. Depending on the symptoms and severity of the bite, treatment can range from supportive care to intravenous administration of antivenom.

“Applying tourniquets, applying ice, suction devices or other measures should not be attempted,” said Keyler. “Get to the hospital is the goal. Antivenom therapy appropriately administered in a timely fashion typically leads to a favorable medical outcome for the patient.”

When it comes to interactions with people, Jones said timber rattlesnakes are actually timid creatures.

“The last thing rattlesnakes want to do is come in contact with people.”

MassWildlife says, “If you are lucky enough to see one of these extremely rare snakes, please let us know! Send an email with any photos and location to natural.heritage@mass.gov.”

Don Lyman is a biologist, freelance science journalist, and hospital pharmacist who lives north of Boston. Send your questions about nature and wildlife in the suburbs to donlymannature@gmail.com.