Plant can't get overfed. And I doubt the ants are damaging the plant. Ants are usually the normal prey for neps, usually ants are attracted by the sugary substance that exude from the plant's peristome & underneath the hood.

Actually ants are one of the top foods for a nepenthes. Nepenthes secrete a sweet smelling nectar that has some sort of a chemical in it that makes the ants drunk like. That causes them to fall into the trap. I would let the ants do their thing but here is a couple things to keep an eye out for.

*Ants are known to farm Aphids and other bad critters for their honey dew. If you see green, clear, or black bugs on the plant. Move the plant and treat it with a safe insecticide.

*Because the plants are eating natural food but not growing in their natural habitat keep and eye out for fungus growing in the traps. If you see any fungus or mold cut the trap off. Also rid the plant of any brown dieing traps.

*Try not to keep the soil water logged. Moist but not too wet. Nepenthes are pretty susceptible to root rot.

*At the end of the growing season all of your outdoor non-dormant variant plants should be secluded and quarantined from your other CP's. This insures that if the plants are sick or have bugs you can easily treat them with out causing havoc on the rest of your collection.

thanks, I was just worried cause the ants were everywhere. Alsoï¼ the ants were fire ant, so will the venom from the ants harm the plant?

The venom in fire ants is there to harm things with a nervous system. Plants do not have that so I wouldn't worry about it. Just keep an eye out for bugs that eat plants.