litterbug n.

c. 1300, "a bed," also "bed-like vehicle carried on men's shoulders" (early 14c.), from Anglo-French litere "portable bed," Old French litiere "litter, stretcher, bier; straw, bedding" (12c.), from Medieval Latin lectaria "litter," from Latin lectus "bed, lounge, sofa, dining-couch," from PIE *legh-to-, suffixed form of root *legh- "to lie down, lay."

Altered in French by influence of lit "bed." The meaning was extended early 15c. to "straw used for bedding" (this sense is early 14c. in Anglo-French) and by late 15c. to "offspring of an animal at one birth" (that is, in one bed). Litter by 19c. had come to mean both the straw bedding and the animal waste in it after use. The sense of "scattered oddments, disorderly debris" is first attested 1730 and probably is from litter (v.) "provide with bedding" (late 14c.) and sense extended from the image of strewing straw.

"insect, beetle," 1620s (earliest reference is to bedbugs), of unknown origin, probably (but not certainly) from or influenced by Middle English bugge "something frightening, scarecrow" (late 14c.), a word or meaning that has become obsolete since the "insect" sense arose, except in bugbear (1570s) and bugaboo (q.v.).

The Middle English word probably is connected with Scottish bogill "goblin, bugbear," or obsolete Welsh bwg "ghost, goblin" (compare Welsh bwgwl "threat," earlier "fear," Middle Irish bocanách "supernatural being"). Some speculate that these words are from a root meaning "goat" (see buck (n.1)) and represent originally a goat-like specter. Compare also bogey (n.1) and Puck. Middle English Compendium compares Low German bögge, böggel-mann "goblin." The sense shift perhaps was by influence of Old English -budda, used in compounds for "beetle" (compare Low German budde "louse, grub," Middle Low German buddech "thick, swollen").

The name of bug is given in a secondary sense to insects considered as an object of disgust and horror, and in modern English is appropriated to the noisome inhabitants of our beds, but in America is used as the general appellation of the beetle tribe .... A similar application of the word signifying an object dread to creeping things is very common. [Hensleigh Wedgwood, "A Dictionary of English Etymology," 1859]

The meaning "defect in a machine" (1889) may have been coined c. 1878 by Thomas Edison (perhaps with the notion of an insect getting into the works). In compounds, the meaning "person obsessed by an idea" (as in firebug "arsonist") is from 1841, perhaps from notion of persistence. The colloquial sense of "microbe, germ" is from 1919.

Bugs "crazy" is from c. 1900. Bug juice as a slang name for drink is from 1869, originally "bad whiskey." The 1811 slang dictionary has bug-hunter "an upholsterer." Bug-word "word or words meant to irritate and vex" is from 1560s.