Here is the full list of all 14 They Came From the Sky achievements.
Abduct 5000 humans
Unlock all Flying Saucers
Throw down 100 Climbers
Blow up 100 Bombermans
Use WARP 100x
Make 1k Combos
Abduct 1000 humans
Abduct 500 humans
Abduct 100 Birds
Abduct 100 Cats
Abduct 100 chickens
Abduct 100 humans
Abduct your first human
Die for the first time