ABDUCTIONS:
Initiate higher chance of our team must retreat / fall back.
Make the aliens drag away alive members of our team.
Display a message box: ALIENS CAPTURED X OF YOUR SOLDIERS
These unfortunates are dragged away and eaten alive.
Hypothetical:
"We could see aliens dragging away soldiers alive or as corpses to make tasty goo-soups from them."
Goal of alien missions could be Gathering Food, because the aliens are growing hungry. So if one of our bases is attacked, then we should panic / stress about how many of our people will be dragged away screaming... just as in aliens to throw some to the Chryssalids.