[Bêthberry]

I am not familiar with The Tolkien Reader, so I don't know how "The Mewlips" is discussed there, but I do have the poem in the collection it was published in, The Adventures of Tom Bombadil.

What is particularly fun about that collection is Tolkien's introduction. He writes a parody of academic or scholarly work, treating these faux-RedBook poems as true academic discoveries of early oral literature. Tolkien posits possible authorship, sources, derivations, etc. Some, he says, were marginalia--scribbled on the edges of the paper around other poems. He identifies one as written by Bilbo, another by Sam Gamgee and a third by "SG". He claims they represent "older pieces, mainly concerned with legends and jests of the Shire at the end of the Third Age." He mentions several of the poems by their numbers (Mewlips is #9), but he does not discuss "Mewlips".

Reading the Introduction is a hoot for anyone who knows the staid, formal, dry tones of academic discussion concerning early texts--Tolkien clearly pokes gentle fun at his own profession but quite possibly at his own creation as well, treating his legendarium to the kind of analysis usually reserved for "real life literature"--the philologist tweaking his own private hobby perhaps. I don't think the man's mind or imagination ever rested.

Copyright does not allow me to type out the entire Introduction, but here are a few passages to give you the flavour of Tolkien's fun.

No. 3 is an example of another kind which seems to have amused Hobbits: a rhyme or story which returns to its own beginning, and so may be recited until the hearers revolt.

The verses, of hobbit origin, here presented have generally two features i n common. They are fond of strange words, and of rhyming and metrical tricks--in their simplicity Hobbits evidently regarded such things as virtues or graces, though they were, no doubt, mere imitations of Elvish practices.

Though the influence of Elvish tradition is seen, they are not seriously treated, and the names used (Derrilyn, Thellamie, Belmarie, Aerie) are mere inventions in the Elvish style, and are not in fact Elvish at all.

I suspect this all makes fun of the scholarly attitude which dismissed Beowufl as serious literature because it included a dragon!

To me, ascribing the dark vision of "The Mewlips" to a particular dark moment in Tolkien's life would be to treat the poem far too seriously and to overlook Tolkien's humour as well as his own interest in recreating a folklore. The Mewlips are creatures much like many of the frightening bogey men in the folklore of early Britain. Here is a link which provides a rather cursory description of many of them:
Mysterious Britain

I would suggest as well that the effort to place the Mewlips themselves within Middle Earth geography is similarly too serious; the work does not appear to have been so seriously related or fixed to the Legendarium.

Or perhaps I should rather say that such endeavour likely could be made, but would be most successful if made in the same vein as Tolkien's own Introduction, as a bit of light-hearted sport!