Kill five worker aliens to unlock this achievement.
Kill 20 worker aliens to unlock this achievement.
Kill 50 worker aliens to unlock this achievement.
Kill 100 worker aliens to unlock this achievement.
Kill 5 arachnid crawlers to unlock this achievement.
Kill 20 arachnid crawlers to unlock this achievement.
Kill 50 arachnid crawlers to unlock this achievement.
Kill 100 arachnid crawlers to unlock this achievement.
Kill 5 alien shock troops to unlock this achievement.
Kill 20 alien shock troops to unlock this achievement.
Kill 50 alien shock troops to unlock this achievement.
Kill 100 alien shock troops to unlock this achievement.
Kill 5 alien rippers to unlock this achievement.
Kill 20 alien rippers to unlock this achievement.
Kill 50 alien rippers to unlock this achievement.
Kill 100 alien rippers to unlock this achievement.
Destroy all of the invading spacecraft and win.