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I think it would be entertaining if we could come up with a list of theorems named after non-human animals (so excluding names like "Gauss's lemma" and the like). So far, I have only encountered two, or if there's more I can't remember them:

$1.$ The Butterfly Lemma (aka the Zassenhaus Lemma in group theory)

$2.$ The Snake Lemma of homological algebra

Is anyone aware of any more theorems named after animals? And if so, why does it have the name it has?

(I'm also not sure as to whether or not I should tag this question as a soft question, as it seems that whether or not a theorem has such a name has an objective answer, but I am happy to edit if need be.)

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    $\begingroup$ I know some theorems named for foodstuffs. the Sandwich Theorem, the Ham Sandwich theorem (they are different), the Pancake Theorem (it is the 2D case of Ham Sandwich), the Pizza Theorem. $\endgroup$
    – user317176
    Jul 10, 2016 at 2:17
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    $\begingroup$ @DougM I guess a lot of those are indirectly named after animals :) $\endgroup$
    – Exit path
    Jul 10, 2016 at 2:18
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    $\begingroup$ excluding names like "Gauss's lemma" and the like Maybe you meant Goose's Llama ;-) $\endgroup$
    – dxiv
    Jul 10, 2016 at 2:51
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    $\begingroup$ How about a book? Abstract and Concrete Categories; The Joy of Cats. store.doverpublications.com/0486469344.html $\endgroup$
    – user4894
    Jul 10, 2016 at 3:00
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    $\begingroup$ Birds On A Wire (maybe). If n birds randomly independently perch on a stretch of wire, what is the chance that each bird is its nearest neighbor's nearest neighbor? This is easily answered with some elementary formulae from Order Statistics. The 2-D version ( birds in a square) was answered in the late 20th century. $\endgroup$
    – DanielWainfleet
    Jul 10, 2016 at 3:22

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The Pigeonhole principle (sorry Russians, I know you name it after Dirichlet and don't talk about the pigeons) is pretty classic:

If there are $n$ pigeons distributed among $m$ holes, at least two pigeons must occupy the same hole when $n > m$.

Now, this is certainly open to some debate: the theorem is really named after the holes, and not the pigeons. But, if the Bridge of Asses counts...

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    $\begingroup$ Ah should've thought of that one, but shouldn't it be when $n$ is strictly greater than $m$? $\endgroup$
    – Exit path
    Jul 10, 2016 at 4:19
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    $\begingroup$ @leibnewtz I kicked myself when I finally did: I upvoted the question when it was initially asked (I think it's fun), but couldn't think of a single example at the time... :) $\endgroup$
    – pjs36
    Jul 10, 2016 at 4:21
  • $\begingroup$ @leibnewtz And yes, I can neither read nor write in my current state, evidently. Thank you! $\endgroup$
    – pjs36
    Jul 10, 2016 at 5:01
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If you're willing to stretch slightly further to philosophy, Buridan's Ass paradox is a good one, especially if the ass is mathematically inclined.

In probability, there's the infinite monkey theorem, because apparently monkeys can't read or write but there can be infinitely many of them.

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The Bridge of Asses (Latin : Pons Asinorum) in Euclid. Here, ass does refer to the animal, not reknowned for its intelligence. The meaning is that an ass cannot cross the bridge (by understanding the theorem). The nuance is the converse: If you can't understand the theorem you are an ass and can go no farther in geometry.

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  • $\begingroup$ I don't remember the theorem being named that way in high school geometry! Probably spared the teacher a headache, or maybe he was an ass himself $\endgroup$
    – Exit path
    Jul 10, 2016 at 4:25
  • $\begingroup$ In the Merriam-Webster dictionary (on-line, via a linked reference in the Wikipedia article Pons Asinorum) it says the first known use of this name for the theorem is in the year 1751. I can understand high-school teachers' avoidance of such terminology in a classroom. $\endgroup$
    – DanielWainfleet
    Jul 10, 2016 at 5:04
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Here are some mathematical theorems or solved problems named after farm animals:

King chicken theorem and other theorems about pecking orders (with chicken comics!)

Archimedes' cattle problem

Goat problem

Then there are mathematical objects (or related algorithms) named after animals:

Caterpillar tree, its cousin centipede graph, and the more distantly related lobster graph

Crocodile dilemma

Hydra game (technically Hydra is mythical so this doesn't count but it's an interesting game.)

Ant colony optimization

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Here are some which, like the other answers, are not all strictly theorems:

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  • $\begingroup$ Not going to lie, I got a pretty big kick out of the Baire category theorem :) $\endgroup$
    – pjs36
    Jul 18, 2016 at 23:44

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