Eels appear in European rivers as glassy, fragile little worms, then they mature and grow up to three feet long. After tracking with satellite tags, researchers can confirm the mature eels leave the rivers to swim to the Sargasso Sea, a unique region of the Atlantic Ocean defined by ocean currents, where they reproduce and then die. After about two to three years, the juveniles make their way back to the rivers of Europe, where the small glassy eels adapt to the freshwater and mature.

Twice a year, snakes, frogs, and other animals migrate between the Shawnee National Forest’s limestone bluffs and its LaRue Swamp area. In between these two areas in southern Illinois stands one major barrier: Snake Road. Car traffic is a major barrier for animal migration, so the Forest Service closes Snake Road to accommodate spring and fall migration, from March 15 to May 15, and from September 1 to October 30.

Measuring just an inch and a half, the globe skimmer dragonfly migrates up to 4,400 miles through the air without landing — flying farther than any other insect on Earth. The globe skimmer dragonfly can fly from India to eastern Africa, traversing the entire Indian Ocean following the weather for the moisture necessary for breeding. When crossing the larger Pacific Ocean, often the dragonflies pause at islands to mate and lay eggs before continuing the journey.

Tarantulas usually stay close to their underground burrows, but each fall, mature male tarantulas of the Colorado grasslands set out in search of a mate. It’s not exactly a migration, as the male tarantula does not have a specific destination, so researchers call it a “mate-gration” or a walkabout. Female spiders remain in their burrows and live for 30 to 40 years, but after mating, the male dies around age 8 to 10.

Leatherback sea turtles have the widest geographical range not just of any turtle, but of any marine reptile. The massive leatherback can grow to be six feet long, and it has a unique rubbery shell. Leatherbacks prefer to eat jellyfish, so they have adapted for deep diving (more than 3,000 feet), and they have adapted to navigate cold water better than other cold-blooded reptiles.

The common cuckoo spends its spring laying eggs in the United Kingdom, then spends most of its winters in central Africa. The lengthy migration includes long uninterrupted stretches of flying over the Mediterranean Sea and the Saharan Desert. While cuckoos lay their eggs in the U.K., but adult cuckoos do not stick around to tend to their young — they drop eggs in other birds’ nests, and the host birds raise the cuckoo chick as their own.

Adult amphibians live most of their life on land, but they start their life underwater. In the spring, amphibians — including frogs, toads, and salamanders — start looking for water, often returning to the same place they were born. They find shallow ponds, or vernal pools that form during spring rains, then spawn clutches of eggs. The tadpoles (or salamander larvae) will eventually mature into land-dwelling adults.

The caribou herds of Alaska and Canada have the longest recorded migration over land. They travel 840 miles per year, which is longer than the entire state of California. After caribou, a group of Russian reindeer travels the second-longest distance, followed by the packs of gray wolves that stalk and hunt the caribou throughout parts of their journey in Alaska and Canada.

Since the 1930s, the town of Capistrano, California has held a festival on March 19 to celebrate the return of cliff swallows to their spring and summer home. But the birds’ appearance at the festival has been less reliable in recent years. A colony of cliff swallows has long nested in the Mission San Juan Capistrano church, but the population never recovered after a renovation in the 1990s.

The term “locusts” has been used to refer to swarms of other types of insects, particularly cicadas, but a true locust is a type of grasshopper. These green insects live like ordinary grasshoppers until they switch into the “gregarious phase,” multiplying quickly and eating all of the vegetation in their path. The swarm usually starts after a big rainfall in a place that usually has desert conditions — most often in East Africa.

Emperor penguins, both male and female, start each year with months of feeding at sea, eating as much as they can. Then, the penguins march about 60 to 100 miles across the Antarctic sea ice, where the females lay eggs. The male emperor penguins keep the eggs in their incubating pouches and huddle together to stay warm during the Antarctic winter. In August, the eggs hatch and the female penguins return.

Several species of lemmings are found in Arctic regions of the Northern Hemisphere, including Norway lemmings. Each spring, water from melting snow floods their burrows and forces them to the surface. The herbivores immediately spread out in search of food, and during heavy breeding years, that migration can turn into hordes of lemmings swarming frantically — and even falling en masse into a body of water.

Hummingbirds do not migrate in a V-formation because they prefer to migrate alone, following the same route of their ancestors. And even if they tried to rearrange themselves, the aerodynamics wouldn’t work for smaller birds. The V-formation works for larger birds with wide wings, as the birds that follow benefit from an upward lift. That helps birds like ducks, geese, pelicans, and cranes conserve energy over long flights.

There are more than a million wildebeest perpetually on the move in the Serengeti region of Tanzania and Kenya. The herd is constantly following seasonal rains to find the best grazing grounds, and sometimes zebras and gazelles join them, too. The wildebeests’ great migration attracts predators — adding hyenas, lions, and others to the swirling circle of life in the Serengeti.

The Christmas Island Red Crab is found nowhere else in the world, but about 120 million crabs live on this small Australian island. During the dry season, the crabs feed on the island’s rainforest floor and stay in the shade or in burrows to ward off dehydration. But in anticipation of the wet season, the red crabs swarm from the forest to their seaside breeding grounds, covering the land in between with a moving carpet of red crabs.

For feeding, humpback whales prefer krill-packed cold waters, but for breeding and birthing, they prefer shallow, warm waters. Humpback whales feed near Alaska, Canada, and Russia, and about half of the humpback whales in the North Pacific then migrate to the breeding grounds of Hawaiian Islands Humpback Whale National Marine Sanctuary. It’s a 3,000-mile journey between the two states, but the whales can make the trip in less than a month.

Each year, arctic terns travel between their breeding grounds in the Arctic Circle and their feeding grounds in the Antarctic Circle. If the tern flew in a straight line, the trip would be over 18,000 miles. But the birds prefer to zig-zag across the Atlantic Ocean, stopping on each side and feeding on fish in between, totalling more than 44,000 miles traveled each year.

In 2015, scientists tracked a female western gray whale, who swam from Russia to Mexico and back again, traveling a total of 13,988 miles in 172 days. The whale named Varvara was tagged near Russia’s Sakhalin Island, and the satellite tracking showed her travel across the north Pacific near Alaska, then follow the western U.S. coast south to Baja California, Mexico.

When Pacific salmon mature, they start their journey upstream to reach their feeding grounds in the Pacific Ocean — a journey that can reach upwards of 1,000 miles. After a lifetime of growing in the Pacific Ocean, salmon return to the riverbed of their birth, lay eggs, and then die shortly after. During the salmon run, the fish fight the current, leaping and dodging dams and predators such as bears.

Unlike other butterflies, the North American monarch butterfly is unable to survive a cold winter. It flies up to 3,000 miles south in the fall to find warmer winters in California and Mexico. But the butterfly that flies south does not return north — these monarchs mate and lay eggs, living a few more weeks before dying. Each subsequent generation travels farther north, taking three to four generations to return north.