Alien seeds hitch a ride to earth in a space shuttle crew and begin to grow. When their numbers reach the Threshold amount they will be an unstoppable swarm.
Signsalien invasion
War of the Worldsalien invasion
Impostoralien invasion
Starship Troopersalien invasion
The Hitchhiker's Guide to the Galaxyalien invasion
The Invasionalien invasion
The Arrivalalien invasion
They Livealien invasion
Independence Dayalien invasion
A Quiet Place Part IIalien invasion
Bugoniaalien invasion
Edge of Tomorrowalien invasion
The Avengersalien invasion
Mars Attacks!alien invasion
Captive Statealien invasion
Man of Steelalien invasion
Avengers: Endgamealien invasion
Elevationalien invasion
Captain Marvelalien invasion
Homealien invasion
Children of MenSame genre & era
The Day After TomorrowSame genre & era
Invaders from Marsalien invasion
Rim of the Worldalien invasion