Largest animal

The average full-grown blue whale (Balaenoptera musculus) is around 20–30 m (65–100 ft) long and weighs c. 160 tonnes (176 tons), though even larger historical specimens have been recorded by both length and weight.

Heaviest: A female blue whale weighing 190 tonnes (418,878 lb) and measuring 27.6 m (90 ft 6 in) in length was caught in the Southern Ocean on 20 March 1947.

Longest: A female blue whale landed in 1909 at the whaling station in Grytviken in South Georgia in the South Atlantic was documented as measuring "107 fot". Based on the Norwegian fot (or "fod") being equivalent to 313.74 mm (as of 1824), this gives a length of 33.57 m (110 ft 1.6 in).

The blue whale is not the longest animal on Earth: that is the bootlace worm (Lineus longissimus), which can reach up to 55 m (180 ft) long.

Newborn calves of the blue whale are 6–8 m (20–26 ft) long and weigh up to 3 tonnes (6,610 lb). The barely visible ovum of the female blue whale (weighing a fraction of a milligram) grows to a weight of c. 26 tonnes (57,320 lb) in 22.75 months (10.75 months' gestation and the first 12 months of life). This is equivalent to an increase of 3x10¹º.

The largest marine animal ever killed by hand harpoon was a blue whale killed at Twofold Bay, New South Wales, Australia, in 1910 that was 29.57 m (97 ft) long.

Unique physical characteristics

Owing to its huge dimensions, with an average body length equivalent to two double-decker buses and weighing akin to 29 African elephants (the largest land animals), almost everything about the blue whale is superlative in some way or another. Among its anatomical records, it can boast the following titles:

• Largest heart: A heart extracted from a 24-m (78-ft) blue whale carcass that washed up on the coast of Newfoundland, Canada, in 2014 weighed 440 lb (199.5 kg); it measured around 5 ft (1.5 m) from the top of the aorta to the bottom of the lowest chamber. The first blue whale heart to have been successfully preserved, it is now on display at the Royal Ontario Museum in Canada.

• Largest lungs: These have a combined capacity of around 5,000 litres (177 cu ft) of air – enough to inflate around 450 party balloons in a single breath! Extremely efficient to boot, its lungs can transfer up to 90% of inhaled air into its bloodstream. By comparison, the equivalent figure on average for humans is a measly 15%.

• Longest penis: The erect penis of the blue whale measures up to 2.4 m (8 ft) – akin to a traditional British telephone box – though accurate measurements are understandably difficult to collect given this organ is very rarely seen.
  Relative to body size, however, there are other animals that are proportionately far more well-endowed. For instance, the Argentine lake duck (Oxyura vittata) has a corkscrew-shaped reproductive organ that measures up to 43 cm (1 ft 5 in), which is equivalent to its entire body length. While in the humble-looking barnacle – those immobile small crustaceans seen clinging to rocks, ships and, fittingly, even whales – penis size can be some 40 times bigger than their shells – a useful adaptation to increase your likelihood of mating when you are unable to move.

• Heaviest tongue: Typically weighs c. 4 tonnes (4.4 tons) – similar to the total body weight of a full-grown black rhino! The area of the tongue would be large enough for around 50 people to stand on it.

Diet and feeding habits

Not surprisingly, the largest animal has an equally large appetite in order to sustain itself – they need to consume between 20–50 million calories per day! The bulk of their diet is made up of small shrimp-like crustaceans called krill; measuring about 5 cm (2 in) long on average, this represents yet another record: the greatest difference in size between predator and prey in the animal kingdom.

To make up for this size difference, the blue whale has to eat a lot of krill – we’re talking around 16 tonnes (17.6 tons) per day! It feeds by gulping in huge quantities of krill-filled seawater – a process known as “lunge feeding”. Interestingly this surprisingly successful approach of hurling itself mouth-first into a vast swarms of smaller prey is thought to have developed with the earliest baleen whales some 10 million years ago and been a key factor that has enabled cetaceans like the blue whale to evolve to their record-setting proportions.

With its cavernous mouth filled with “krill soup”, the whale then lifts its titanic tongue to the roof of its mouth, pushing the water back out. The krill aren’t going anywhere, however, with the majority ensnared in long bristles (the so-called “baleen” that this family of whales are named after) that hang from the top of its upper jaw, before ultimately being devoured.

Reproduction and life cycle

Unlike many other cetaceans, blue whales tend to lead a solitary lifestyle, occasionally forming small groups in areas with a rich food supply. Although much about their courtship, reproduction and pregnancy habits is still a mystery, we know that females reach sexual maturity between five and 15 years of age. With a gestation period of around 10–12 months, these whales typically give birth to a calf every two to three years; the mother will stay with the infant for about a year.

Even the day that they are born, blue whales are setting records. Measuring 6–8 m (19–26 ft) long and weighing 2–3 tonnes (2.2–3.3 tons) their calves are easily the largest offspring in the animal kingdom. And they grow up quick: guzzling more than 190 litres (50 gal) of 40–50% milk every day in its early months, by the end of its first year, a baby can have put on almost 33 tonnes (36 tons) in bodyweight!

Threats and conservation status

With a global population of 10,000 to 25,000, blue whales are currently classified as Endangered by the International Union for the Conservation of Nature. While this may sound like quite a lot, it’s less than 10% of the worldwide total around the turn of the 20th century. Their numbers were decimated for many decades by commercial whaling (primarily to extract oil from their blubber), though since being designated a protected species in 1966, their fortunes do seem to be improving.

They still face other threats, though, particularly as our oceans get ever busier. Some of the biggest dangers they face in the 21st century are strikes by ships, getting tangled in fishing gear and marine noise pollution, which can disrupt their communication and migration habits. As with almost all sea life, they are also affected by climate change; as Earth’s polar ice melts and oceans warm, all whales – including blues – are having to adapt their behaviour in order to seek out diminishing and geographically shifting krill colonies, as well as new shallow areas to raise their young calves as sea levels rise.

5 quick facts about the largest animal in the world

1. Despite their name, blue whales are really coloured more of a mottled grey – but they gain a bluer tint underwater.
2. The blue whale has a typical lifespan of 80–90 years; the oldest known specimen reached 110.
3. They have the slowest heart rate in a mammal; when diving deep, it can slow to as little as four to eight beats per minute!
4. Their booming vocalizations (up to 188 dB) can be heard by other blue whales hundreds of miles away. Their songs are the second-loudest animal sounds, only surpassed by the 236-dB clicks produced by sperm whales (Physeter macrocephalus).
5. A blue whale can excrete c. 200 litres (53 gal) of crumb-like poop in one go! Their waste serves as a valuable fertilizer for marine algae, which in turn is what their own food (krill) feeds on, so theirs is a very sustainable diet.
   
   

Frequently Asked Questions

Is any animal bigger than the blue whale?

Although widely recognized – for good reason – as the all-time largest animal, depending on what metric you are using to determine size, there are a few other creatures that could be argued to surpass this gargantuan marine mammal – at least in length, if not bulk.

One contender is the largest jellyfish – the lion’s mane jellyfish (Cyanea capillata) – whose extremely long, stinging tentacles can trail as far as 36.5 m (120 ft) behind its “bell”, akin to the length of three and a half school buses! Then there’s the even longer bootlace worm (Lineus longissimus): a 55-m-long (180-ft) specimen was washed ashore at St Andrews in Fife, UK, in 1864, following a severe storm. This makes it the longest solitary animal on record.

When we say “solitary”, there are also what are known as “colonial animals” that can reach even greater lengths, though like jellyfish tentacles and worms, they all tend to be quite long and thin in body shape, so nowhere near as massive as whales.

One such example of colonial animals are jellyfish-like marine organisms known as siphonophores. The largest of these ever observed was a specimen of the ribbon-like Apolemia uvaria (known colloquially as the “long stingy stringy thingy”!), which was spotted off Western Australia in 2020 and estimated to have had a staggering total length of 119 m (390 ft). Laid out straight, that would stretch across almost two and a half Olympic swimming pools. But as colonial animals are, in fact, lots of smaller creatures that live together it’s not really fair to compare them like for like with singular life-forms.

If factoring in extinct animals, other megafauna are occasionally proposed to have rivalled or even exceeded the blue whale, but so far such claims have largely been treated with scepticism. One recent example, first officially described in 2023, is a form of early whale dubbed Perucetus. Although “only” thought to have reached a maximum of 20 m (65 ft) long, researchers argued that its bone density could have meant its weight ranged from 85 to as much as 340 tonnes (94–375 tons), the upper range of which would be more than double that of a typical blue whale and potentially make this the heaviest animal ever. But as the huge range in mass indicates – in tandem with criticism received after the research was published – more evidence is needed before Perucetus can conclusively take this record from B. musculus.

What are the largest land animals alive?

Compared to a blue whale, the largest living terrestrial animals are almost pipsqueaks – but of course everything is relative. Adult male African bush elephants (Loxodonta africana) are huge from our perspective, typically weighing 4–7 tonnes (4.4–7.7 tons) and standing 3–3.7 m (9 ft 10 in–12 ft 1 in) to the shoulder. If factoring in height, then another African giant takes the crown: male giraffes (Giraffa camelopardalis) can grow to between 4.6 and 5.5 m (15–18 ft) from hoof to ossicones (furry horns), making them the tallest animals that exist today.

What is the biggest land animal to ever exist?

Venturing back into prehistory, there were, of course, much larger animals that used to walk our planet that have long been extinct. Among mammals, there were mastodons, straight-tusked elephants and the rhino-like Paraceratherium that may have stood up to 4.8 m (15 ft 9 in) tall at the shoulder and weighed in excess of 18 tonnes (19.8 tons) – so more than three times the mass of a modern elephant.

But dwarfing the biggest ever mammals were, of course, the mega reptiles of the Mesozoic, the “age of the dinosaurs” that lasted from 252 to 66 million years ago. While the precise scale reached by the largest dinosaurs has long been debated (and probably always will be), there’s no doubt that plant-eating sauropods were the biggest animals ever to walk on land. A subset of these, known as titanosaurs (such as Argentinosaurus and Patagotitan), were giants among giants. Conservative estimates suggest they could have reached 30–40 m (98–131 ft) long, as tall as a six-storey building and weighed in the region of 50–75 tonnes (55–83 tons).

New methods and formulae are often being devised to assess the fossilized bones of sauropods – especially as new ones come to light – and as such the scope of how big they could get fluctuates. Recently one study even posited that some “super sauropods” may have even rivalled the blue whale in mass but there many varied views on this hypothesis.

Is a blue whale bigger than a Megalodon?

Although we can only estimate the size of the largest shark ever based on a few fossilized bones and teeth, it’s safe to say that the blue whale outsized it. However that’s not to take away from what a fearsome predator this ocean giant would have been when it was around some 20–3.6 million years ago. Conservative estimates suggest that the Meg (Otodus megalodon) would have reached at least 15–18 m (50–59 ft) long, and perhaps as much as 20 m (65 ft). This also makes it a prime contender to have been the largest fish ever too. Megalodon literally translates as “big tooth”, which is apt: the longest Megalodon tooth found to date was about the same length as a TV remote!