Meet the Most Important Animal You’ve Never Seen

By | January 22, 2020


[intro ] In 1913, a scientist named Nathan Cobb wrote the following: “If all the matter in the universe except
the nematodes were swept away, our world would still be dimly recognizable
… we should find its mountains, hills, vales,
rivers, lakes, and oceans represented by a film of nematodes.” He wasn’t writing a horror story, and he wasn’t exaggerating. The world really is covered by tiny, unnoticed roundworms. And it’s worth paying them some notice. Because Cobb was right: we’re pretty much waist deep in them everywhere
at all times. And they’re doing a lot more than you might
think. Some nematodes can be deadly. Others might save the world. Here are seven reasons nematodes are worth
paying attention to. First of all, what is a nematode? Well, it’s a worm — but a lot of animals are worms. Earthworms belong to a different group entirely: the segmented worms. Then there’s flatworms, the group that includes tapeworms. And depending on who you ask, there’s a lot of other worm-like groups
out there too. Only some of the things we call “worms”
are nematodes, which scientists place in the phylum Nematoda. Not that that narrows it down much. That phylum still represents a lot of worms. And by a lot, I mean nematodes basically run
this show. It’s their world. You’re just living in it. Let’s put it into horrible, horrible perspective. Right now there’s a little less than eight
billion people on planet Earth. By contrast, there are 57 billion nematodes. Not total, though. 57 billion… for every human on Earth. That’s 438.9]million trillion nematodes. That estimate is for soil nematodes, by the
way. There could be even more that don’t live
in soil. Put differently, according to one estimate, four out of every five animals that live on
our planet are nematodes. So do me a favor go out into the woods and collect all the nematodes from one square
meter of habitat, you’d probably have several million. Yet these things are barely noticeable. You don’t see a horror movie-worthy mass
of squirming invertebrates every time you open the front door. That’s because most nematodes are tiny — often microscopic. Still, the combined weight of all the nematodes
on Earth is around 300 million metric tons, which equals around 80% of the combined weight of all the world’s
humans. We’re not sure how many species of nematodes
there are, but estimates range from a few tens of thousands into the millions, of species! A lot of these species are undescribed because there are more nematodes than nematode
scientists, by a lot. But maybe we should be devoting more study
to our nematode overlords. Depending on who you ask, a single pair of rats may produce 15,000 descendants
in a single year. But it’s nothing compared to what nematodes
can do. The large intestinal roundworm, for example, can lay as many as200,000]eggs… in a single day. These particular nematodes can also store
as many as 27,000 eggs in their bodies at one time. Like, imagine if chickens could do that, we’d all eat nothing but omelettes. And that wasn’t enough for them, not all nematodes stick to a scheme of male
and female for reproducing. The well-studied nematode C. elegans has males and hermaphrodites capable of fertilizing
themselves — but no females. A related species referred to as Rhabditis
SB347 – This is how we have to name nematode species
– has three sexes: males, females, and hermaphrodites. Having more mating partners available — including yourself, for the hermaphrodites
— creates a ton of flexibility. They can find partners — or a single hermaphrodite pioneer can go forth
and multiply. Because there aren’t enough nematodes already. Whatever their sex, nematodes are built for
breeding. An adult C. elegans only has about a thousand
somatic or non-reproductive cells in its body. But it may have a roughly equal number of
germ cells devoted to reproduction. So if you’re a nematode, a pretty big percentage of your body is just
dedicated to making more nematodes. Still, they can’t be everywhere, right? There are lots of places where life is sparse. Maybe you could escape the worms by moving
to the Arctic or something. But no, you can not. There are at least two species of nematode that are specifically adapted to living in
Arctic ice — at least one of which eats other nematodes,
by the way. So if you really dislike creepy-crawlies, you can’t escape to the far north. Nor the far south. The most abundant land animal in Antarctica’s
polar desert is… wait for it… a nematode. And they’re everywhere in between. Some nematodes also thrive in hot, dry conditions. Some, in fact, can live in places that are
totally inhospitable to humans and most other animals. Like Mono Lake in the eastern Sierra Nevada
Mountains, which is the saltiest lake in California. It also contains enough arsenic to make it
dangerous for humans and fish. In a 2019 study published in the journal Current
Biology, researchers identified eight species of arsenic-resistant
nematode. All eight species found in the lake can tolerate about 500 times the amount of
arsenic that would kill a human being. So they don’t mind the cold, they don’t
mind the heat, and they don’t even seem to care too much
about being poisoned. Nematodes aren’t especially shy, either. They enjoy the company of other animals. Some of them like to share a meal. Because they’re intestinal parasites. So they literally will share your meal, you
know, after you’ve eaten it. Others prefer to live in close company with
other species. Like the hookworm, which also thrives in innards, but doesn’t bother with intestinal contents
— instead, juveniles live off of the blood and
tissue of their host. Not all nematodes are parasites, but some scientists think parasitic species
may number around 25,000]— and those are just the ones that parasitize
vertebrates In fact, some researchers think that one out of every two animals has its own parasitic
nematode, which cozies up to no other type of animal. How sweet. Humans got lucky. We have around sixty nematode species that
like to parasitize us, though we get to share at least some of those
with other organisms. Capillaria philippinensis, for example, usually parasitizes birds, but humans can get it from eating certain
kinds of fish. That can happen when we eat the fish, instead of the normal bird predators that
the nematode counts on for its life cycle. Humans can become infected with Trichinella,
too — but so can pigs and feral hogs, mountain lions,
and bears. And a parasitic nematode infection isn’t
just gross; some can be deadly. Especially if left untreated. Move over, viruses, there’s a new friend
in town. Nematodes’ planetary domination isn’t
new. At least, we don’t think it is. Nematodes have soft bodies and they decay
rapidly, so they’re not commonly found in the fossil
record. Even so, the oldest-known nematodes date to
four hundred million years ago. Some scientists think nematodes have been
around a lot longer than that, though, for at least a billion years. If that’s true, it means they evolved just
after bacteria, protozoa, and fungi, and way before pretty much everything else. The first parasitic nematodes probably evolved
from free-living marine nematodes — they likely evolved to parasitize marine invertebrates. So not only have they been around since the
dawn of multicellular life, some of them have been getting a free ride
off of other organisms the whole way. Now nematodes are really basic life forms
— really, they’re just tubes that digest food
with a few other rudimentary organs thrown in there. But they’re still animals, like us. They’re simple, and yet there’s a seemingly
endless variety of these things. And not all of them follow the “microscopic
and innocuous” model. Some of them get weird. The biggest nematode Placentonema gigantissima can reach between eight and nine meters in
length. It also lives in the placenta of a sperm whale,
so there’s that. Some of them even have “fur”. It’s actually a thick layer of bacteria
that oxidizes sulfur, which makes it possible for this particular
type of nematode to survive in sulfur-rich habitats on the
ocean floor. They do creepy things, too. Nematodes pee through their skin, for example. Kind of. Humans and other mammals excrete nitrogen
waste in urine. Nematodes can’t be bothered to wait in line
for the restroom, so they excrete nitrogen waste directly through
their body wall. Also, some nematodes have amoeboid sperm — which means it doesn’t swim, it crawls. So despite the fact that their basic body
plan is just… a gut, they manage to be pretty weird. Nematodes have also taught us a surprising
amount of what we know about our own bodies. In particular, C. elegans, that well-studied
species we mentioned earlier, is widely used for biological research. Scientists like this particular nematode because
each adult has a fixed number of cells. What’s more, those cells develop according
to the same pattern every time, which makes it possible for scientists to
follow the fate of each and every one as the organism develops from an embryo. Even though C. elegans is a very simple creature, many of its genes have functional counterparts
in larger animals like humans. Nematodes also share some of the same biological
characteristics as humans. Like some of the same tissues: skin cells,
neurons, muscles, and others all passed down to both humans
and nematodes from a common ancestor. Research using C. elegans has led to a lot
of really important breakthroughs, like discoveries about human kidney disease, and improving our understanding of cancer. C. elegans was also the first multi-cellular
organism to have its entire genome sequenced. And because C. elegans produce more than a
thousand eggs a day, with a life cycle lasting only two weeks, they can provide scientists with a never-ending
supply of themselves. We kind of have to love nematodes, or at least acknowledge their worth. Because not only are they medically important
— they can help us in other ways, too. In fact, they can teach us a lot about the
most important scientific challenge of our time — the climate. Nematodes are major players in the carbon
cycle. They exhale roughly two percent of soil carbon
emissions — emissions that come exclusively from organisms
that live in soil. That’s roughly equivalent to 15 percent
of the carbon we emit through fossil fuels. They also respond to changes in temperature
and precipitation in really important ways. For example, a 2019 study found that drought conditions
in grasslands can harm populations of predatory nematodes. That leads to an increase in their prey: nematodes
that eat grass roots. And that can have a snowball effect — in a negative way — on grass growth. When root-eating nematodes over-eat, the grass weakens and dies. Meanwhile, microbial respiration releases
even more carbon into the atmosphere. Which means even subtle changes to the climate
can be amplified… via the effects on nematodes. Just because the things being affected by
climate change are microscopic, doesn’t mean the consequences can’t be
felt. So we have to keep nematodes in mind when building our understanding of climate
change. Yeah, the whole “film of nematodes” thing
is kinda gross. Things that writhe and squirm and live in
your guts aren’t usually very high on most people’s
lists of favorites. Thankfully, most nematodes are so tiny that
they’re functionally invisible. But that doesn’t mean you can ignore them, because they’re also really, really huge. In more ways than one. Thanks for watching this episode of SciShow, and thanks to our patrons for making it happen. We are pretty sure we have the coolest community
of supporters ever, and they make it possible for us to provide
free educational videos for everyone. If you want to get involved, head on over
to patreon.com/scishow. [ outro ]

100 thoughts on “Meet the Most Important Animal You’ve Never Seen

  1. Daniel Campbell Post author

    Have there been ways of testing for nematodes on other celestial bodies? Have we checked the moon or Mars?

    Reply
  2. Kobe Beef Post author

    I'm surprised hank didnt talk about pinworms also known as thread worms. They live in human intestines and come out of the butthole at night laying eggs and causing anal itching. It infects 30-50% of the global population.. some countries advise deworming every 6 months due to these guys

    Reply
  3. Michael S Post author

    I learned a cool nematode fact recently. There is a nematode species that makes the vitamin B-12. Many animals have evolved a symbiotic relationship with this nematode, one of which is humans. Unfortunately, our B-12 nematodes live in our small intestine and the B12 they make can't be absorbed. Lucky for us, though, ruminates, like cows, can absorb the nematodes' B12. B12 deficient humans still have B12 in their feces, because it's made in our gut, just not absorbed. This is not an endorsement of eating your own poop for B12, though.

    Reply
  4. Aviendha Post author

    All praise our nematode overlords. Also ew, I kinda hate these parasites.

    Reply
  5. sanjay shinde Post author

    But most successful class is arthropods. They are abundant in no. Mostly insects

    Reply
  6. Keb Lee Post author

    Oh i didn’t like this one. Especially since he didn’t reassure me that they’re benign or that its unlikely that we have one without knowing. Uuggghhhh.

    Reply
  7. Anton-Constantin Post author

    we're like nematodes, programmed to live, to survive and destroy

    Reply
  8. Greg Hartwick Post author

    Who was it that said “We’re all nematodes on this bus”? Winston Churchill, I think.[he may have been drunk, at the time]

    Reply
  9. 4Dmike Post author

    Plenty of references to sponge bob but no mention of Doug…

    Reply
  10. Andrei Tudor Post author

    What Happens if you stuck ~infinity of microscopic nematodes? Will you be able to see them?

    Reply
  11. NerdNr5 Post author

    Do I have to give this video a thumbs up? I really didn't like what he said. Can I pls have a new reality without parasites?

    Reply
  12. Mohd Ameerzah Post author

    I have a confusion , we read that arthropoda is the biggest phylum followed by the mollusca
    How come nematodes are being regarded as most numerous?

    Reply
  13. Vince S Post author

    My Parents are the most Important! Ps. Cracking Video ~ Cheers

    Reply
  14. Michael Donovan Post author

    They keep saying that perhaps a billion animals have died in Australia’s wildfires, but they just mean vertebrates. For invertebrates, the number is probably trillions upon trillions.

    Reply
  15. sdfkjgh Post author

    3:50 "Bisexuality automatically doubles your chances of finding a date for Saturday night."
    –Woody Allen

    Reply
  16. Justin Marino Post author

    I wonder if nemotodes were at least partly responsible for the Dust Bowl in the 1920s.

    Reply
  17. Jack Kraken Post author

    I don't think those nematodes share food with us, more like they are freaking parasites.

    Reply
  18. Jen G Post author

    Imagin being the first human to come face to … face, with the whale placenta worm…

    Reply
  19. pencilpauli Post author

    Q: What do you get if you cross a clownfish with a frog?

    A: A Nemotoad

    Reply
  20. Morgan Biddlecom Post author

    I saw the thumbnail but didn't check the channel and I thought I was in for an episode of Microcosmos. I thought I was going to get to meet some nematodes just chilling under a slide.

    Reply
  21. wiadroman Post author

    "They just tubes that digest tubes with few other organs threw in there" – sounds like my spirit animals.

    Reply
  22. Joe Hunter Post author

    This goes to show we were placed on this earth and aren't from here we there's tons of things to be discovered

    Reply
  23. Bingo the Pug Post author

    “Doug Bags a Nematoad” was the very first episode of Nickelodeon’s Doug back in the early 90’s.

    Reply
  24. Ashley Santiago Post author

    How many people immediately thought of Spongebob when they watched this episode?

    Reply
  25. Mattteus Post author

    Man, nematodes are way cooler than the show Doug led me to believe!

    Reply
  26. Bryna Waldman Post author

    AOC has an asteroid named after her, because of doing research on nematodes more than a decade ago. This is from wikipedia;
    "She came in second in the Microbiology category of the Intel International Science and Engineering Fair with a microbiology research project on the effect of antioxidants on the lifespan of the nematode C. elegans.[19] In a show of appreciation for her efforts, the MIT Lincoln Laboratory named a small asteroid after her: 23238 Ocasio-Cortez."
    The contest she participated in was a national science contest for high school kids. Pretty cool.

    Reply
  27. S M Post author

    Thanks, now I’ll remember this when I’m outside or eating

    Reply
  28. Claudio Nervi Post author

    where's the "but why is my anus covered in nematodes?"?

    Reply
  29. Minnesota Fatz Post author

    They remind me of the things in "The Supernaturalist" by Eoin Colfer

    Reply
  30. Princess IronLove Post author

    Well, since we're on the topic on Nematodes I have a question . . .

    Are pinworms (Enterobius vermicularis) Anaerobic or Aerobic?

    Reply
  31. PARKER LEWIS Post author

    I have a whole bunch of flatworms in my aquarium are they nematodes I can see there eyes

    Reply
  32. frank234561 Post author

    Roger Klotz is still to this day looking for those nematodes.

    Reply
  33. Jeffrey Streets Post author

    There is no climate catastrophe coming. Just another cycle… you brainwashed idiots. Geesh! 😬

    Reply
  34. Maya Thomas Post author

    “57 billion? I mean that’s a bunch but not.. that much.”

    per person

    “… o”

    Reply
  35. tristan san roman Post author

    Dude how do tardigrades fit into this picture????!!!!

    Reply
  36. The Brocialist Post author

    No One:
    Nematodes: Hungry…. Hungry! Hungry! Hungry! Hungry! Hungry! Hungry!

    Reply
  37. Christierney 71 Post author

    So… are you always wearing a condom

    Asking for a friend

    Reply
  38. Troy Richards Post author

    oh shoot, are we starting to say less than 8 billion rather than over 7 Billion? we're closing in on that 9 Billion limit!

    Reply
  39. Sgt Kozak Post author

    grown up guy that believes 00.012% increase of CO2 can change catastrophic climate change? how sad… the channel should be renamed to ScamShow

    Reply
  40. bohba13 Post author

    That smell, that smelly smell, the smell of… Nematoads.

    Reply
  41. Brian Jones Post author

    Actually, I have seen a nematode. Spotted a giant (close to a cm long) nematode of unknown species in my driveway on a dark night. Silly thing had phosphorescent bacteria in it's digestive track that gave away it's position.

    Reply
  42. Rasmus Post author

    Did he just use the metric system? One small step for Hank, one giant leap for USA

    Reply
  43. LagiNaLangAko23 Post author

    Mentioning Antarctica and nematodes give me X-Files flashbacks.

    Reply
  44. LagiNaLangAko23 Post author

    Everyone talking bout Spongebob's house. Just be thankful they didn't crawl into Spongebob's body holes.

    Reply
  45. Vigneshwaran Renganathan Post author

    Branchiostoma did you forgot to include this specie?

    Reply
  46. Random Guy Post author

    Maybe it isn't that impressive when you consider the fact that they're a phylum.

    Reply
  47. Ufasdfgewaf Post author

    3:47 i kinda expected apache attack helicopter as the third sex

    Reply
  48. Joseph Hargrove Post author

    Banish the fruit flies! With this much genetic variability, coupled with their genetic simplicity and rapid rate of reproduction, the new king of the evolutionary laboratory must needs be crowned.
    richard hargrove

    Reply
  49. scifiaudious2 Post author

    SOME NEMATODES PRODUCE MORPHINE AND MORPHINE LIKE CHEMICALS

    Reply
  50. Deadite Post author

    Huh, the estimate for nematode species is the same for parasitic species, every 4 out of 5 (out numbers other animals 4 to 1). Neat.

    Reply
  51. Iago Silva Post author

    1:42 Hey, baby – quality over quantity any day but Thursday

    Reply
  52. Sally Griffin Post author

    They also get eaten by the fungus that connects trees in a forested area. COOL!!!

    Reply
  53. klutterkicker Post author

    "4 out of every 5 animals are nematodes" glances over at five of my coworkers…

    Reply
  54. Evi1M4chine Post author

    C. elegans. Literally the gayest animal on the planet! 😀

    Reply
  55. bleachno9 Post author

    People keep saying Spongebob but my old ass just remembers Doug

    Reply
  56. DreHeyHer Post author

    Before i saw this video the only thing i knew about nematodes is that they ate spongebob squarpants' house.

    Reply
  57. Andre Leal Post author

    If their total mass is less than the total mass of humans, as said in the video, then this still is an ant's world, I'm afraid.

    Reply
  58. omnigeddon Post author

    damn so informative… explains the floods in africa and the impact of temp changes in the indian ocean which in the end is causing the insane weather in oz wow crazy stuff

    Reply
  59. LordOfTheCats Post author

    C. Elegans is the first organism to be (partially) simulated in a virtual environment. Look up the OpenWorm project and SIBERNETIC

    Reply
  60. Prowler Cam Post author

    "There are more nematodes in heaven and earth, Horatio,
    Than are dreamt of in your philosophy."

    Reply
  61. Prowler Cam Post author

    There may be nematode sperm crawling through you right now…

    Reply
  62. Ginny Jolly Post author

    PLEASE tell me that the nematodes normally in humans are successful in that they don't harm their hosts. I am cool with them living in me AND BEING MICROSCOPIC! But I don't want to know that they will overrun our bodies like trichinella, hook worms, and platyhelmenths (*shudder*).

    Reply
  63. Ginny Jolly Post author

    By the way, trichinella is why we cook pork to doneness, and why beef really should be done so the same way.

    Reply
  64. Varad Mahashabde Post author

    Update : there are about a 0.8 billion more people now in 9 years, and the next billion will be in about 4

    Reply
  65. Steve Jenks Post author

    Word on the street is that the first syllable is pronounced "nem" not "neme". This is a common error, so don't feel too bad.

    Reply

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