Middle English souken, from Old English sucan "draw liquid into the mouth by action of the tongue and lips," especially "draw milk from the breast or udder," from Proto-Germanic *suk- (source also of Old Saxon sugan, Old High German sugan, Old Norse suga, Danish suge, Swedish suga, Middle Dutch sughen, Dutch zuigen, German saugen "to suck"), from PIE root seue- "to take liquid," perhaps imitative, the source also of Latin sugere "to suck," succus "juice, sap;" Old Irish sugim, Welsh sugno "to suck." Compare sup (v.2). Related: Sucked; sucking. 

In reference to blood by mid-14c., of biting flies, etc. To suck the blood of figuratively as "to exhaust" is by 1580s. The disdainful slang expression suck eggs is attested by 1906, earlier is the expression teach your granny/grannum to suck eggs (1732), "said to such as would instruct any one in a matter he knows better than themselves" [Grose]; a suck-egg (c. 1600) was "a young fellow," also "silly person," but also an avaricious one, the last from the image of animals (especially the weasel) reputed to suck eggs. Sucks (n.) as an expression of contempt (sucks to you) is by 1905.

The meaning "do fellatio" is recorded by 1928. The slang sense of "be contemptible" is attested by 1971 (the underlying notion is felt as fellatio).

To suck hind tit "be inferior" is American English slang recorded by 1940.

The old, old saying that the runt pig always sucks the hind teat is not so far wrong, as it quite approximates the condition that exists. [The Chester White Journal, April 1921] 

also blood-sucker, late 14c., "an animal that sucks blood," from blood (n.) + sucker (n.). Originally especially medicinal leeches. In the figurative sense, of persons, "extortioner, sponger, one who preys on others," it is attested from 1660s. Related: Bloodsucking.

1890s, "one who does fellatio" (especially a male homosexual); 1920s as "contemptible person," American English, from cock (n.1) in phallic sense + sucker (n.). Used curiously for aggressively obnoxious men; the ancients would have recoiled at this failure to appreciate the difference between passive and active roles; Catullus, writing of his boss, employs the useful Latin insult irrumator, which means "someone who forces others to give him oral sex," hence "one who treats people with contempt."

also sucker-punch, 1926, from sucker in the "dupe" sense + punch (n.3). Figurative use by 1929. As a verb by 1942. Related: Sucker-punched.