There are two kinds of beings in the universe: those that are Brood, and those that aren’t. Although it sounds like a cliché, when it comes to the Brood, truer words were never spoken. In 1982, on the heels of the science-fiction explosion of the late 70's, Chris Claremont and Dave Cockrum introduced into the Marvel Universe the Brood, an insect-like alien race initially allied with the villainous Shi'ar princess Deathbird. A hive-minded hierarchy of imperialistic parasites intent on overrunning the universe with their offspring, the Brood made their intentions quite clear right away: proliferation of their kind. The Brood reproduces in a manner most horrifying. They forcibly implant their eggs into other sentient organisms. Upon hatching, the Brood egg overtakes and transforms the body of its host incorporating its mind, persona and genetic material into the Brood—essentially killing them. Those the Brood don’t deem fit to host their eggs, they eat or enslave.
While the origins of the Brood are unknown, one doesn’t need to understand their starting point in order to see where they’re headed if left unchecked. Psylocke said it best in Contest of Champions II #3:
“The Brood are predators. They believe in manifest destiny on a cosmic scale. All creation is theirs for the taking.”