One of the mysteries of the Marvel universe is exactly what went into the serum that transformed the frail Steve Rogers into the mighty Captain America. The serum’s secrets died with its creator Abraham Erskine, of course, but in at least one continuity, it was based on the blood of Spider-Man.
First off, yes, this would normally be impossible due to the Star-Spangled Avenger ascending decades before Peter Parker was born, but this particular tale involves time travel, thus throwing chronological limitations out the window.
Marvel 1602 is an 8-issue limited series where an unknown event caused superheroes to begin appearing centuries earlier than they should have, instigating a potential collapse of reality. The plot involves intrigue at the courts of the English queen Elizabeth I and the Scottish king James VI, with several characters standing in for historical figures, such as Doctor Strange replacing magician John Dee, Nick Fury taking on the duties of spymaster Francis Walsingham and Magneto heading up the Spanish Inquisition instead of Tomás de Torquemada.
Peter Parker (or Parquagh, to be specific), is also present as Fury’s apprentice, although doesn’t receive his powers until the end of the story. He appears in two of the three sequel books, 1602: The New World and Spider-Man: 1602, and in the latter of these takes center stage.
Suspected of being a witchbreed (mutant), he’s captured by natural philosopher Henri le Pym and drained of blood with leeches, which Pym’s employer Baron Octavius intends to use to cure himself of an affliction that transformed him into a hideous octopus man. The ensuing battle between a number of heroes and villains of variously shifting allegiances results in the destruction of Pym’s lab, and seemingly all trace of his work. However, the penultimate page reveals that a vial of Peter’s blood was discovered centuries later in a Venetian dungeon, which proves the key to creating the super soldier serum, the strength, speed, agility, reflexes and healing it imparts being dilutions of the superhuman levels Spider-Man possessed.
Following the resolution of the initial miniseries, the primary 616 Marvel continuity was returned to normal and a pocket reality designated Earth-311 was created by Uatu the Watcher, in which all subsequent events play out. So, while the mainstream Captain America has no connection to Spider-Man, in this reality, a closed time travel loop resulted in the wall-crawler ultimately allowing Cap to become the super soldier of legend.
