Practice English Speaking&Listening with: What Animal Dominates Earth?

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Ask any casual science enthusiast what animal group has more species than any other, and theyll probably say beetles.

And there are a ton of beetle speciesmore than 350 thousand, in fact.

Thats about 22% of all species that weve identified and named so far, including stuff like bacteria.

But some scientists think beetlestime at number one should come to an end.

Other animal groups, they say, may be more deserving of the title ofmost species”.

Though its tough to say which group that actually is, and its not just about knowing for curiositys sake.

Having good estimates of how many species of beetle, plant, or bird there are is vital to tracking how those numbers are changing, and what we have to do to preserve them.

Its hard to actually pin down how many species there are for a couple of different reasons.

One is that species estimates are based on the number of species we currently know about, and were not familiar with an equal proportion of every group of animals.

It depends on how interested we are in them and how easy they are to find.

Beetles in particular were a popular collectors item with old-timey naturalists, who gathered them for their exciting array of colors.

And that interest meant there was ample funding and opportunity to go look for more beetles.

Meanwhile, less charismatic animals, or ones that were smaller and harder to count, missed out

Animals like Hymenoptera, the group of insects that includes sawflies, wasps, bees, and ants.

A 2018 paper published in the journal BMC Ecology argued that there are more species of hymenopterans than anything else, thanks in large part to parasitoid wasps.

And if youre thinking of the yellowjackets in your garden, think again.

These wasps can be barely bigger than a grain of sand and spend most of their life cycle inside other insects, making them very easy to miss.

Parasitoid wasps target pretty much all insects, including ones that live in the ocean, in the Arctic, and deep down in the soil.

And scientists think that these wasps are pretty specialized, meaning each species only targets a specific type of host.

So according to the 2018 study, every insect, including all those beetles, might have not just one but potentially multiple species of parasitic wasp hunting them down.

Also, insects have multiple life stages, and different wasps can target both the larval and adult forms.

So two wasps for every beetle? I mean, you do the math.

Thats not even counting parasitoids that target other parasitoids or ones that go for non-insect arthropods, like spiders.

And its not just one study making this claim.

Studies of sand dunes in California and insects in Canada estimate that hymenopteran species outnumber beetles by about two and a half times in that particular habitat.

Now, if hymenopterans are not the most speciose animal groupthats the technical term for having a lot of speciesits probably still some sort of parasite.

And thats because parasitism is really popular in the natural world, evolving more than 200 separate times in 15 different groups of animals.

And it makes sense! Hosts are both food and shelter rolled into one.

That makes nematodes, or roundworms, another contender for the most species-rich group.

Not all nematodes are parasites, but many are and they target not just insects, but also other animals and plants.

One 1993 study estimated there may be well over a million nematode species, though other estimates have varied wildly because theyre so understudied.

Another paper from 2008 suggested that there may be between 75,000 and 300,000 species of nematodes parasitizing vertebrates alone.

And nematodes have been found everywhere, including sediments deep down on the ocean floor.

Theres probably nematodes in places humans have never even been yet.

Which is an important point: species estimates rely on what we can find, which means they rely on where humans can go.

Now, you may have noticed that were comparing nematodes, which are an entire phylum of worms, to wasps and beetles, which according to the tree of life are technically orders.

You know, kingdom, phylum, class, order.

But even if you compare whole phyla, nematodes could still win out over arthropods, the phylum that contains wasps and beetles.

We think theres roughly a million of each, but theres so much variation in those estimates that its tough to call.

And we dont assign those groupsphyla, classes or ordersbased on how big they are, but thats a whole other story.

And then theres the question of charisma, which could explain why Diptera, the order that includes true flies, have been overlooked.

They might grab your attention when theyre buzzing around your living room, but there arent many people whod say theylike flies.

Not like people like beetles.

But when scientists do get to studying them, they find a surprising number of species.

Like a study from 2018 that found more than 4000 species of true flies in a four-hectare patch of Costa Rican rainforest.

Current estimates put Diptera at more than a million species, easily surpassing beetle numbers.

Theres that million number againI mean, we told you it was tough to call.

Flies can live almost anywhere on land and, as larvae, can feed on everything from plant nectar to vertebrate blood.

And thats important too: for a group of animals to stand a chance at being the most speciose, it has to show variety in where it lives, what it eats, and how it survives in general.

And that could mean making yourself comfortable inside a host like a parasite does, or being able to find homes in some of the most remote places on Earth.

But, if theres anything weve learned from trying to count all of the animals, its that whats right in front of us isnt always a good indicator.

If we want to know whats out there, weve got to go look for it.

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