In A MARK TWAIN LEXICON, edited by Ramsay and Emerson (1963), they give
“alkali-spider” an AB1 designation which indicates “Mark Twain is the sole
authority for a word or meaning that is not found in OXFORD at all ...” p.
xii. They go on to state that the word “Alkali” itself in OEDS 1907 refers
to “One who lives in or frequents an alkali region.”

A further search of historical newspaper databases did not turn up any
other stories, writers, or editors using the phrase.

Barb