On one tragic night in the summer of 1967, two young women were killed by grizzlies in two separate attacks inside Montana’s majestic Glacier National Park.

The two women, both 19 years old and both employees at two of the park’s lodges, embarked on overnight backpacking trips with friends on August 12. Unknown to them, grizzlies had been spotted near lodges and campsites in the park for weeks, attracted to food left behind by careless campers and even fed to the animals by photo-seeking tourists.

Back in the 1960s, there were no bear-proof garbage cans and few other safety precautions at U.S. national parks to alert visitors to the presence of bears. The two victims, Julie Helgeson and Michele Koons, slept outside under a canopy of stars without a clue that their campsites were about to be raided by hungry and aggressive grizzlies.

Helgeson and a friend were awoken in the pre-dawn hours by a large grizzly sniffing at their sleeping bags. They tried to play dead, but the grizzly sunk his teeth and claws into both of them and dragged Helgeson away as she screamed for help. She was found hours later by a search party, badly wounded, and died before the rescue helicopter reached the hospital.

Koons and her friends had more warning, but a similar awful outcome. Their camp was raided by a grizzly as they cooked dinner, but thinking the animal was sated, they moved down to a beach to spend the night. The bear returned at 4:30 a.m., and while her friends were able to clamber up nearby trees, Koons was brutally mauled—the bear bit off her arm. She succumbed to her injuries before help arrived.

The gruesome attacks, chronicled in the 1969 book Night of the Grizzlies by Jack Olsen, led to widespread policy changes at U.S. national parks to prevent the feeding of animals, remove trash and close campsites and trails where bear activity was spotted.

The Japanese island of Hokkaido is home to a hulking subspecies of brown bear called ussuri that can grow larger than a grizzly. They can also be deadly aggressive, with 86 ussuri attacks recorded on Hokkaido since 1962, including 33 fatalities.

But the worst bear attacks in Japanese history took place over a harrowing week in December of 1915 when a ravenous bear awoke early from hibernation and went on a killing spree in the frontier outpost of Sankebetsu that ended with seven people dead, mostly women and children.

The hungry and agitated bear, which weighed 750 pounds and measured nine feet long, killed its victims by stalking them in their homes. Even when the town assembled an armed security squad, it was unable to stop the almost-daily attacks. The bear was wounded multiple times by gunfire, but kept returning to claim more victims, including a pregnant woman and an infant.

Finally, professional bear hunters were called in to kill the bear. Traumatized, most of the villagers moved away from Sankebetsu where a shrine stands today to commemorate the lives lost in this brutal and historic attack.

Timothy Treadwell made a name for himself as a “friend” of the grizzly bears in Alaska’s Katmai National Park, where he documented his startlingly close relationship with these majestic and much-feared animals.

For 13 years, Treadwell spent his springs and summers in the park, filming himself having playful interactions with wild grizzlies, which he called by pet names like Crackers and Mr. Chocolate. Without any wildlife training or particular expertise, Treadwell dubbed himself a “protector” of the grizzlies and was featured in magazine and TV profiles.

Tragically, his most famous appearance came in the 2005 documentary “Grizzly Man,” which chronicles how Treadwell’s obsession with grizzlies came to a horrifying end. On October 5, 2003, Treadwell and his girlfriend Amie Huguenard were mauled and killed by a starving grizzly bear in their tent.

Chillingly, Treadwell had his camera rolling, but because the lens cap was in place, only the audio survived. Filmmaker Werner Herzog, who directed the documentary, is one of the few people to hear the disturbing recording. Once he did, Herzog suggested that it be destroyed.

In 2011, a group of British teenagers were on a month-long arctic adventure in Norway, where they hoped to catch a rare glimpse of a polar bear in the starkly beautiful landscape. But no one expected such a dreadfully close encounter, one that claimed the life of a 17-year-old boy with dreams of becoming a doctor.

Young Horatio Chapple was one of 80 students taking part in an expedition to Svalbard, Norway organized by the British Schools Exploring Society (BSES). The teens were excited to explore the remote wilderness, make new friends and study the effects of climate change on the Arctic environment.

Polar bears are a known threat in Svalbard, but parents had been assured that all participants would be equipped with pen flares to scare off bears and that the campsites would be ringed with tripwires that set off small explosive mines. They were also told that one adult group leader would carry a firearm.

When the expedition hit the ice, however, the team realized there weren’t enough pen flares to go around, and some of the tripwires weren’t working properly. The gun carried by Chapple’s group leader was an old rifle that the adult leaders weren’t well trained to use.

As fate would have it, a starving polar bear entered Chapple’s camp unnoticed while the teens slept. It ripped into Chapple’s tent and bit one of his companions on the head before mauling Chapple, who was dragged from the tent and killed. In addition to Chapple’s death, four other members of the exploration party were seriously injured by the polar bear, including two adult leaders who struggled with the rifle before finally killing the desperate animal.

The Liard River Hot Springs Provincial Park in British Columbia, Canada, is a paradise amidst the boreal forest, where locals and tourists flock for a dip in its steaming hot pools. On August 14, 1997, Patti McConnell and her two kids needed a break from a long road trip from Texas to Alaska and decided to pull over at the hot springs.

McConnell and her 13-year-old son, Kelly, walked down the boardwalk and up some stairs to explore a less-crowded pool. That’s when McConnell heard a rustling in the underbrush and turned to stare down a large black bear. She was barely able to yell out to Kelly before the bear tackled her and began to viciously maul her.

Despite his size, Kelly kicked the bear in the face and beat it with a tree branch to try and save his mother, but the bear clawed him across the neck and lifted him into the air by his waist before tossing him aside in a heap.

Hearing their cries, a bystander named Ray Kitchen rushed to the scene and also tried to beat the black bear away from its two bloodied victims. The bear turned on Kitchen and struck him with such force that the two went tumbling through a railing and down a hillside, where the bear fatally mauled Kitchen in the neck.

Another man was critically wounded before two more bystanders rushed in with hunting rifles and killed the rampaging animal. While McConnell also died from her wounds, her brave young boy survived, and Kelly and Kitchen (posthumously) received medals of courage from the Canadian government.