Fatness is not unique to us humans. There are plenty of supersized animals out there.
But determining which animal is the fattest isn’t as straightforward as it may appear.
As the largest animal in the world, the blue whale (Balaenoptera musculus) also has the most fat. In a 1968 study involving 49 different species of mammal from across the US and Brazil, researchers deduced that the blue whale had the highest percentage of body fat – more than 35%. With the whales weighing in at up to 180 tonnes, that’s easily a record-breaking amount of fat for one animal.
But if we look at things proportionally, you might be surprised by some of the world’s full-fat species.
We’ll begin with blubber, the fat rich tissue belonging to marine mammals that has myriad benefits for streamlining, buoyancy, defence, insulation and energy storage.
Among the whales with the thickest blubber are the so-called right whales (Eubalaena). They are popularly thought to have earned this common moniker during the bloody era of whale hunting in the 19th Century.
There’s lots of lipid in the gut, tongue, bone
“They are slow and fat and when harpooned they float for easier retrieval. Most other whales sink,” says Dr Sam Ridgway, president of the National Marine Mammal Foundation, explaining how they were considered the ‘right’ whales to hunt.
The whales float because they have a high percentage of lipids, or fat, in their blubber. There are three species of right whale, found in the North Atlantic, North Pacific and Southern Oceans. These docile animals once swam close to boats but now they are among the most endangered animals in the world. They were hunted to near extinction for their oil which was used in everything from soap, to lamps and even margarine.
In waters further north live bowhead whales, the Arctic specialists. To survive in these frosty, remote waters they have a layer of blubber almost half a metre (2 feet) thick. In his studies, Dr Craig George found blubber mass ranged from 43% to 50% of the body mass of yearling whales.
Hippos are known for their dumpy appearance
“However, there’s lots of lipid in the gut, tongue, bone etcetera so total percentage [fat] for these animals is quite a bit higher than the blubber percentage suggests,” says Dr George.
Pinnipeds, the family of animals that includes seals and walruses, might also be considered candidates for the title of world’s fattest animal.
Freshly weaned pups in particular can reach high body fat percentages after feeding on their mother’s milk, which is extremely rich in fat. The pups of elephant, hooded, harp and ringed seals can reach 50% fat at weaning. But this literal puppy fat doesn’t last.
Camel humps are nutritional stores of fat that can weigh up to 35kg
Staying close to the water, walruses might look chubby, but measurements of adult females in Greenland found they were 18% blubber and 44% muscle. Likewise, hippos are known for their dumpy appearance, but 18% of their impressive 1.5 tonne weight is actually skin. Beneath this 5cm (2”) thick hide hippos have a relatively thin layer of fat.
Sometimes you need to look a little more closely at land animals to find the fattest ones.
For example, the beaver stores its considerable fat reserves in its large tail. Apart from a few bones, ligament and muscles, the tail is mostly fat and can reach 45cm (18”) long and 20cm (5”) wide.
Much like the whales’, the beaver’s oil reserves made it a target for hunters in the past. Fortunately now the species is making a comeback thanks to reintroduction schemes. But the animal’s habit of gnawing down trees and damming rivers can cause controversy. The beaver feeds on trees, grasses and aquatic plants through the summer but needs stored energy to help it through the winter.
Moths and their larvae have long been known to Aboriginal Australians as fat-rich snacks
Piling on the pounds to survive cold temperatures is a common trick among mammals.
In the frozen Arctic, polar bears can have fat reserves that account for half of their total body mass. They achieve this by feeding on the blubber of marine mammals and weaning their cubs on milk that is almost 30% fat.
The fat not only keeps them warm but when it metabolises, fresh water is produced which is essential in the polar desert.
This leads us onto camels, which live at the other end of the temperature spectrum.
Their distinctive humps are not full of water but are actually nutritional stores of fat that can weigh up to 35kg. Overall though, camels are lean animals, with most of their body fat concentrated into their humps. The theory is that this reduces insulation over the rest of their body which helps them cope with their hot environment.
Curiously some of the fattest land animals relative to their size are found in an often overlooked group of insects.
Moths and their larvae have long been known to Aboriginal Australians as fat-rich snacks. Kidney specialist nurse Lesley Salem worked with a team to produce a guide to the nutritional values of bush tucker to aid in nutritional advice. The report describes how the larvae of the cossid moth (Endoxyla leucomochla), aka the witchetty grub,is 20% fat while the adult bogong moth (Agrotis infusa) is almost 39% fat.
But the animal that is proportionally the fattest of all might not be what you’re expecting.
In Yellowstone National Park, grizzly bears are known to gorge themselves on army cutworm moths before winter sets in.
These insects are known in the prairies of the western US where their mass emergence in spring can cause an agricultural nuisance. Around June they migrate to alpine climates where they feed on the nectar of wildflowers. The moths fatten up over the summer to an extraordinary extent, reaching a whopping 72% body fat by the autumn.
“Basically fat is the storage mechanism by which insects that engage in migratory flight obtain their energy. Some insects might fly over 100 km in a single day without feeding, thus they need a large energy reserve,” explains entomologist Dr Todd Gilligan from Ohio State University in the US.
Much like Australia’s bogong moths, army cutworm moths have a long journey to complete and at the end of it they must be fit enough to reproduce.
It’s a true tale of survival of the fattest.
See Do fat animals have heart attacks? by BBC iWonder