#1 Realize this about feeding your plant:
1) Consider a bug fertilizer to the plant ( this is in fact what it is ). In the wild the soil that these guys/gals live in is bare of all substance. Very poor soil. So the plant has created a way to get what every other plant can get.
If you 'fertilize' your plant, it will grow faster, bigger, stronger
If you don't 'fertilize' it will still grow, just not as fast, not as big ( or it will take longer ) and not as strong.
So feeding is really an optional thing. OF course if you feed it anything it will grow, but NOT feeding will have the same effect.
#2 The plant will enjoy soft bodied insects. Flies, Mosquitos...things that do not have a hard shell. Some people have bad luck with Spiders and Ants. Sometimes Ants will try to get their 'friend' out of the trap, and in the process cut up the plant. Plus they are too small for the plant.
Whatever you feed it make sure it: 1) is alive- nothing dead. 2) is small enough to fit into the trap. You want the trap to be able to close tight aroung the prey.. If space is left open around the trap, sometimes bacteria can get in and kill the trap. 3) I would stay aways from poisonous insects- spiders, ants.
#3 Refer to the top
If you are going to feed it ants, I would be very careful not to have the plant around the ant bed. Ants can emmit scents to attract others to their where abouts. NOT GOOD FOR THE PLANT.