Written by: Liz Langley
Born laid-back: The three-toed sloth under the lens is calm and calm.
摄影：JOEL SARTORE, NATIONAL GEOGRAPHIC CREATIVE
"Why are sloths so slow?" Recently, Vittorio Colonna questioned us via Facebook. Sloths may be slow-moving animals in the forests of Central and South America, but they are not alone, and there are many species in the animal kingdom that live loosely. So, this week's bizarre animal highlights a few slow-moving species, so why did they win the evolutionary race?
Sloths are the most slow-moving mammals in the world, crawling up to 1.6 kilometers per hour. Arboreal life deprives them of the ability to live on the ground, and generally can only hang on trees, moving forward alternately on all fours, at an extremely slow speed.
Sloths " move just enough to keep the energy in balance," Becky Cliff, a zoologist at the Sloth Shelter in Costa Rica, said in an email. They have a slow metabolism and "every move must be carefully planned." "Sloths have incomplete thermoregulation, which affects their digestion. It takes an average of 16 days for food to be digested through the digestive system. Warmer climates can slightly speed up digestion, Cliff said in a study published in April. As the temperature rises, so does the amount of food the sloth eats.
Because it usually hangs upside down on the branches, the sloth's hair is fluffy, grows backwards, and the hair is green with algae attached to it, so the sloth becomes a master of camouflage, mixing in the canopy to easily avoid predators. Today, "big cats and horned eagles are extremely rare, and there are few natural enemies of sloths." But "slow action can still help them keep them out of sight of predators." So camouflage is especially important for sloths," Cliff said.
A laid-back lifestyle can be dangerous. Many slow-moving animals cannot escape predators, so they evolve traits that make it difficult for predators to catch or swallow.
Its own armor is the best defense, such as turtles or turtles have turtle shell protection. "With turtle shells on your back, you have to be slow to move," said Jeffrey Lovech, a reptile expert at the U.S. Geological Survey's Southwest Center for Biological Sciences. In the case of desert turtles, for example, their average speed is 0.3km/h. Although the shell causes slow movement, it is extremely defensive, which is why the desert turtle can live on Earth for more than 200 million years.
Slugs and snails are both molluscs that have lived on Earth for more than 550 million years and have never received an "overspeed fine.". Slugs and snails move forward on muscle contractions at an astonishingly slow pace. Similar to turtles, snails also have a protective shell. Slugs and snails are infested at night and secrete disgusting mucus, which provides them with additional safety.
"In general, if animals are chased or chased by other prey, they evolve to become faster and more agile," Chris Barnhart, a biologist at the University of Missouri, explained in an email. Of course, "fast" is a relative concept. Rose snails are able to follow the mucus trajectory of other snails or slugs, "rushing forward" at a speed of 0.0016km/h. The smell of predators also alerts other snails, who will try to "escape" and speed up slightly (though the poor little guy didn't escape in the end).
According to the American Museum of Natural History, slugs do not have a protective shell like snails, but they secrete "richer and more viscous mucus." Mucus is very powerful, and both domestic cats and dogs try to avoid it.
The manatee is a herbivorous marine mammal that inhabits the coasts or rivers of the sea and can swim at speeds of up to 8km/h, said George Burgess of the Florida Museum of Natural History. The manatee has tough skin and is so large that even its natural enemy, the white shark, can only bite its tail, and it is nonsense to eat the manatee at once.
Manatees are slow in movement, but their skin is hard and thick. Above, a Florida manatee stares blankly at the camera in the Middle of the Vicki river.
Photographed by BRIAN SKERRY, NATIONAL GEOGRAPHIC
Nudibranchs are a group of brightly colored marine soft-bodied shellfish that are "unusually beautiful" but slow to move and can only move 10 meters a day, Burgess said. Nudibranchs are able to use the toxins drawn from their prey against predators.
A 2012 study published in the Journal of Experimental Marine Biology and Ecology showed that greenland sharks were the slowest-moving sharks, leisurely wandering the sea at a speed of 1.22 km/h. The shark is "6 meters long and has a very low metabolic rate," Burgess said.
Greenland sharks are not a problem with their defenses, and attacks are extremely threatening. They often sneak up on seals resting in the water. Seals are agile, and to ensure a successful capture, Greenland sharks lurk at the mouth of holes in the ice, waiting for prey that jumps into the water, "and the prey is caught as soon as it enters the water." ”
(Translator: Strange Flowers Blossom)