"restlessly impatient," 1838, American English, from plural of ant + -y (2); probably reflecting the same image as the slang expression have ants in (one's) pants "be restless and fidgety" from a century later. Related: Antsiness.
c. 1500 shortening of Middle English ampte (late 14c.), from Old English æmette "ant," from West Germanic *emaitjon (source also of Old High German ameiza, German Ameise) from a compound of Germanic *e-, *ai- "off, away" + *mai- "cut," from PIE root *mai- (1) "to cut" (see maim). Thus the insect's name is, etymologically, "the biter-off."
As þycke as ameten crepeþ in an amete hulle [chronicle of Robert of Gloucester, 1297]
Emmet survived into 20c. as an alternative form. By a similar contraction, aunt "a parent's sister" is from Latin amita. White ant "termite" is from 1729. To have ants in one's pants "be nervous and fidgety" is from 1934, made current by a popular song; antsy embodies the same notion.
adjective suffix, "full of or characterized by," from Old English -ig, from Proto-Germanic *-iga- (source also of Dutch, Danish, German -ig, Gothic -egs), from PIE -(i)ko-, adjectival suffix, cognate with elements in Greek -ikos, Latin -icus (see -ic). Originally added to nouns in Old English; used from 13c. with verbs, and by 15c. even with other adjectives (for example crispy).
Others are reading
<a href="https://www.etymonline.com/word/antsy">Etymology of antsy by etymonline</a>
Harper, D. (n.d.). Etymology of antsy. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/antsy