Freezer. Just freeze it for a few hours or over night, so it's dead (they can survive at least half an hour in the freezer). They're not getting fragile, just carefully put it into the tube while still frozen. Ants prefer soft-bodies fragile food anyway.
Small spiders (just frozen) are really really good ant food (they're hunters so they are full of tasty insect protein), like up to twice the size of a fruit fly (not bigger, the huge ones will just scare the queen).
First time I gave my ants a small spider (when they were four ants) the queen grabbed it and ate it alone.
Found some old pictures - it was like the T-Rex ripping through that goat.
So yes, spiders are a delicacy (and usually easy to find), I've seen no insect-eating ant species so far that didn't absolutely
love them.