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To say that the earthworms are essential to the health of the planet Earth would be a gross understatement. So much so that there is no way that I can list you all their benefits at once. But what about in an alternate Earth where earthworms became extinct?

56 million years ago, the Paleocene-Eocene Thermal Maximum lasted three to four times longer than it did in our timeline. The problem regarding earthworms wasn't a change in climate--it was actually overdiversification. They had become so specialized that any change in the environment, no matter how minor, could collapse the whole system. Everyone in every system overreached their peak too quickly due to the longer PETM, including the earthworms. 36 million years ago was this alternate Earth's date for the Icing of Antarctica (known more formally as the "Azolla Event"), and 14 million years ago, the global temperature dropped so dramatically and so suddenly that half of all plant and animal species went extinct. Here is a list of animal groups that I have found to bear the closest similarities to earthworms in regards to size, habitat and niche:

  1. Apoda--the caecilians, a group of serpentine, legless amphibians. They live more sheltered lives than the frogs and salamanders, so they are the least studied amphibian order.
  2. Scolecophidia--the blind snakes
  3. Diplopoda--the millipedes
  4. Chilopoda--the centipedes
  5. Insect larvae that have evolved to be neotonous--in other words, they have evolved beyond the need to complete their metamorphic stages.

The real question isn't deciding which of the animals listed above would be best qualified to refill the earthworm niche, but would all of them occupy the earthworm niche at once?

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    $\begingroup$ I think the norm is for only one organism to occupy a niche after enough time has passed since it outcompetes all the others. You should only find multiple organisms in a single niche if that niche was new or recently wiped clean. $\endgroup$
    – DKNguyen
    Aug 18, 2020 at 0:43
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    $\begingroup$ How geographically dispersed are these thousands of species? $\endgroup$
    – DKNguyen
    Aug 18, 2020 at 1:04
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    $\begingroup$ @DKNguyen Like I said, cosmopolitan. $\endgroup$ Aug 18, 2020 at 1:07
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    $\begingroup$ I think you are misunderstanding my question. Earthworms having thousands of species and being cosmopolitan doesn't mean that I'm going to find ten different species of earthworms in my backyard. The same type of niche, in two different locations is two separate niches. $\endgroup$
    – DKNguyen
    Aug 18, 2020 at 1:08
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    $\begingroup$ Actually, the traditional earthworm wasn't present in North America prior to european settlement, and the Americas did okay. Without earthworms, soil has more organic material in it, and earthworms alter the soil, making it less able to retain water, nutrients, especially in forests. en.wikipedia.org/wiki/Earthworms_as_invasive_species $\endgroup$
    – DWKraus
    Aug 18, 2020 at 16:20

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No

The most well-known role of earthworms is to break down dead plant matter so it can be reabsorbed into the food web. Amphibians, snakes and centipedes all tend to be carnivorous so those won't work. Milipedes on the other hand are usually herbivores so they present a possibility.

I mean a worm is just the logical conclusion of a millipede right, in the limit when legs become infinitely numerous and infinitely small?

The problem is that millipedes do not burrow. So they will only recycle in the top layer of the soil, leaving whatever it is earthworms usually do deeper down undressed.

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  • $\begingroup$ With a vacant niche, milipedes could evolve to burrow. Might take long, but then again earthworms didn't always exist either. $\endgroup$ Aug 18, 2020 at 1:34
  • $\begingroup$ @Renan Since all the earthworms suddenly died I presume the question is whether any of the species can step into their role quickly. $\endgroup$
    – Daron
    Aug 18, 2020 at 1:43

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