Which is larger, giant squid or the Moon?

Ha ha tricksy title! I mean giant squid as in multiple giant squid, Architeuthis dux not a single giant squid, which would be a very silly question indeed. I’ll explain how I got to this question first as it probably isn’t one that many people have contemplated.

Cartoon by Mark Carnall of a moon made of cephalopods

Calamari Moon by Mark Carnall (Own work) CC BY 2.0 but let me know if you do!

I’ve been reading the excellent book- The Search for the Giant Squid by Richard Ellis which gives a comprehensive account of the biology and mythology surrounding giant squid, Architeuthis dux and related species up to 1998. The book covers the earliest accounts of encounters of giant squid; an examination of tall tales about large cephalopod encounters; giant squid in literature and film; and a really nice history of giant squid models in museums. Despite being one of the largest living invertebrates, very little is still known about giant squid including how their arch-enemies, the not-so-small-themselves cetaceans, sperm whales, catch them.

In the dark depths of the ocean how do essentially blind, breath-holding, large sperm whales catch highly manoeuvrable, fast, super-sensed giant squid? How do they catch them with their weird toothed mandible especially considering that giant squid retrieved from sperm whale stomachs don’t have any bite marks? And what does any of this have to do with the Moon?

Ellis’ history of the giant squid presents a series of tall tales and unverifiable encounters which will be familiar to anyone who follows cryptozoology. Historical accounts of encounters are unreliably recounted, embellished and changed over time or don’t match up with official shipping records. For the encounters where a specimen of a giant squid was washed up or in fewer instances collected, there are nearly always complications. Giant squid carcasses have a history of being fed to dogs, getting used for fish bait or falling apart when fished from the sea. Then for the specimens that do beat the odds and make their way into collections, the usual smorgasbord of museum-destroying natural disasters means that there’s still precious little material in museums to give us insight into these creatures. In 1998, Ellis lists 166 authenticated giant squid sightings and strandings. GBIF lists 117 Architeuthis dux specimens in museums, a list that is most certainly incomplete.

With little in the way of a physical record, or reliable historical record, fundamental questions about the size of giant squid populations are surprisingly difficult to answer. Giant squid are rarely caught in nets, despite their size (another where are the cephalopods mystery), and a good part of our record of their populations, numbers and sizes come from examining stomach contents of sperm whales.

Quite how sperm whales hunt giant squid is still a matter of conjecture. Sperm whales have to breathe air, so quite how on a big breath, in the deep ocean, under pressure, in the dark, they manage to snare the giant squid in their tweezer-like jaws is a puzzle.

By Julian Ilcheff Borissoff (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons

Sperm whale mouth. WEIRD. Image Julian Ilcheff Borissoff (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)%5D, via Wikimedia Commons

Sperm whales have a very weird narrow mouth, they only have teeth in the lower jaw, which slot into fleshy pockets in the ‘upper jaw’. Various theories have been proposed for how they hunt giant squid including attracting them with glistening white teeth, attracting them with bioluminescent squid juice on their teeth or stunning them with ultrasound blasts and then using their jaws to scoop them up off the ocean floor. They might suck them up in a twisting vacuum which is still an aquatic acrobatic feat but hasn’t been convincingly confirmed as their prime hunting behaviour. However, they accomplish the feat of catching them, they do catch them as can be confirmed from partially digested bodies and isolated giant squid beaks found in sperm whale stomachs.

Working in 1977, biologist Malcolm Clarke who researched cetacean-cephalopod interactions tried to estimate the mass of giant squid in the ocean by back-of-a-fag-packet calculations by estimating how many giant squid are eaten by sperm whales as the population of sperm whales is slightly easier (although still not perfect) to estimate than for cryptic giant squid. Now I may normally err on the pedantic side when it comes to science and communicating science but I do have a lot of time for aforementioned fag packet estimations and calculations, the wackier and more improbable the comparison the better.

Using a 1973 (generous?) estimate of a population of 1.25 million sperm whales with an average weight of 15 tons for males and 5 tons for females, Clarke calculated that there was roughly 10 million tons of sperm whale mass in the ocean. Clarke assumed that each whale eats ten times it’s weight in giant squid a year, giving the guestimation of 100 million tons of squid a year eaten by sperm whales (Clarke 1977 summarised in Ellis 1998). Which Ellis points out is larger than the biomass of annual world catch of ‘fish’ by fishermen (which was close to true in 1998, but in 2016 makes up just over half of global World fisheries ‘production’). It is also the estimated biomass of the human population.

I’m getting to the moon.

Another legendary cephalopodologist, Clyde Roper, repeats this calculation in an interview for Smithsonian magazine in 1996, estimating a million or so sperm whales eating 3 or 4 giant squid a day- ergo a lot of giant squid to sustain them (Roper 1996 summarised in Ellis 1998, this may be part of that article at Smithsonian magazine).

In a footnote to this period of giant squid biology, Ellis references a letter to the editor (summary reprinted in New Scientist) of the Smithsonian magazine, from the Calamari Legal Institute expressing shock at the “cataclysmic calamari ingestion of 547500000” giant squid per annum assuming that half of all sperm whales eat 3-4 giant squid a day. The fictional Institute further calculating that this would mean that sperm whales eat 80% of the volume of the Moon in giant squid (got there) a week assuming an average volume of 11 cubic metres per giant squid.

Unfortunately for the Calamari Legal Institute, the tongue in cheek parley was flawed as, sometimes happens to the best of us, they’d mixed up 5 billion cubic feet and 5 billion cubic miles when estimating the volume of the Moon.

The spoilsport who pointed this error out, Gary D.Garrett, noting “Insatiable sperm whales could not consume a
calamari Moon, therefore, in billions of years”.

20 years on from this science funny business, we’re still not much the wiser when it comes to sperm whale or giant squid population estimates. According to the IUCN Redlist page for Sperm Whales today’s sperm whale population is modelled between 400,000 and 600,000 individuals. With the deeply flawed model above, this gives us an estimated 2,000,000 giant squid eaten a day, or 22 million cubic metres of giant squid. Coincidentally this is the exact same amount of squid a day eaten by sperm whales, as the water consumption in Metropolitan Athens per year in 1940 or if you prefer, the same as the volume of water held in the Lister dam in Germany, one of the dams targeted by British Royal Air Force Operation Chastise in 1943. I’m sure there are other meaningful comparisons to be made.

Based on the above calculations give or take a few, 1997090909x1018 giant squid make up the same volume as the Moon which would take today’s sperm whales roughly 3.6 billion years to eat assuming all sperm whales eat at least 3 individuals a day.

So now you know how long it would take today’s sperm whales to eat a calamari Moon and in answer to the original question above, the moon is much, much larger than all the giant squid that have ever lived put together in a tentacly ball in space.


Clarke, M.R. 1977. Beaks, Nets and Numbers. Symposia of the Zoological Society of London. 38:89-126.

Ellis, R. 1998. The Search for the Giant Squid. Penguin Books Ltd.


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