You know what I think? I think beholders have a tadpole stage in which they float around, wriggling tails downward, taking in the world around with their one combination eye-mouth.
I'm pretty sure they metamorphose by sweet-talking intelligent thralls (abetted, naturally by their burgeoning charm person rays) into building them secure nests.
Ahh, there's a similar idea already in the canon--it didn't know mind-flayers used tadpoles, but apparently you can use them to mash them up with beholders:
Witness the mindwitness (that's kind of a crappy name):
You can get d20 stats for it here. Scroll down about 55% of the page.
And I finally discovered The Annex. Their beholder article is here.
They don't seem to have an article on Lickitung, however. For that, visit Bulbapedia here.
P.S. Leave it to Google Image Search to teach you that anything can be naughty, even something as innocent as this guy: